Name: _______________________________________________

CS C1 F Formulae, hazards and equations

Date:

Time: 31 minutes

Total marks available: 31

Total marks achieved: ______

BRI

Questions Q1.

A technician made some dilute sodium hydroxide solution by carefully adding some solid sodium hydroxide to pure water. This is the hazard symbol on a bottle of solid sodium hydroxide.

(i) State what this symbol shows about sodium hydroxide.

(1)

.............................................................................................................................................. (ii) Sodium hydroxide solution reacts with dilute hydrochloric acid. During the reaction heat is released. What type of reaction is this?

Put a cross ( ) in the box next to your answer. (1)

A displacement

B endothermic

C neutralisation

D precipitation Q2.

A student is investigating the maximum mass of sodium chloride that can be dissolved in 100 cm3 water at room temperature.

The student has been given 1.0 g samples of solid sodium chloride to dissolve in the water.

Draw one straight line from each substance to its state symbol.

(2)

(Total for question = 2 marks)

Q3.

A student is investigating the maximum mass of sodium chloride that can be dissolved in 100 cm3 water at room temperature.

The student has been given 1.0 g samples of solid sodium chloride to dissolve in the water.

Which row of the table shows the correct formula of sodium chloride and of water?

(1)

(Total for question = 1 mark)

Q4.

These two hazard symbols are attached to a container of liquid bromine.

A chemist uses bromine in an experiment.

Use the hazard symbols to suggest safety precautions the chemist should take when using the bromine.

(2)

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

Q5.

Elements in the periodic table

(a) Copper is a metal.

(i) Complete the sentence by putting a cross ( ) in the box next to your answer. In the periodic table copper is in

(1)

A group 0

B group 1

C group 7

D the transition metals (ii) Which of these is a property of copper metal?

Put a cross ( ) in the box next to your answer. (1)

A does not conduct an electric current

B forms colourless compounds

C has a low melting point

D is malleable

(b) Helium and argon are noble gases.

(i) Choose the correct word from this box to complete the sentence below.

(1) Argon can be used to put out fires because it is .......................................................

(ii) Choose the correct phrase from this box to complete the sentence below.

(1)

Helium is used in airships because it .......................................................

(c) Chlorine, bromine and iodine are halogens.

(i) The table shows the appearance of bromine and iodine at room temperature.

Complete the table to show the appearance of chlorine at room temperature. (2)

(ii) Chlorine reacts with hydrogen to form hydrogen chloride.

Write the word equation for this reaction. (2)

................................... + ................................... → ...................................

(Total for question = 8 marks) Q6.

Write the balanced equation for the combustion of methane, CH4, in oxygen to form carbon dioxide and water.

(3)

.............................................................................................................................................

Q7.

Calcium nitrate solution reacts with sodium carbonate solution. The products are calcium carbonate and another salt.

Write the word equation for this reaction. (2)

.............................................................................................................................................. .............................................................................................................................................. Q8.

(a) Hydrogen chloride, HCl, can be formed by the reaction of hydrogen, H2, with chlorine, Cl2.

Write the balanced equation for this reaction. (2)

.............................................................................................................................................

(b) The electronic configuration of hydrogen is 1. The electronic configuration of chlorine is 2.8.7.

Draw a dot and cross diagram to show the arrangement of electrons in a molecule of hydrogen chloride, HCl. Show outer electrons only.

(2)

Q9.

Barium reacts with chlorine to produce barium chloride, BaCl2. Write the balanced equation for this reaction.

(2) ............................................................................................................................................. Q10.

In the Haber process nitrogen and hydrogen are reacted together to form ammonia. The balanced equation for the reaction forming ammonia is

(i) All substances in this reaction are in the same physical state.

Give the name of this physical state. (1)

..............................................................................................................................................

(ii) State the meaning of the symbol in the equation. (1)

.............................................................................................................................................. .............................................................................................................................................. Q11.

Unreactive metals are found as uncombined metals in the Earth's crust.

When iron oxide is heated with carbon, iron is produced.

(i) Complete the word equation for the reaction.

(2) iron oxide + carbon → ........................................................... + ...........................................................

(ii) What happens to the iron oxide during this reaction?

(1)

A the iron oxide burns

B the iron oxide is neutralised

C the iron oxide is oxidised

D the iron oxide is reduced

(Total for question = 3 marks)

Examiner's Report

Q1. (i) This question was generally answered well and scoring the mark. Unfortunately, several candidates were giving two or sometimes three HAZCHEM descriptors or contradictions that meant the mark could not be awarded. More worrying were answers of the type 'Sodium hydroxide is an acid….'.

Results Plus: Examiner Comments Many candidates were mixing the descriptions for the hazard symbols. 0 mark was given for the answer 'toxic'.

Results Plus: Examiner Comments Several candidates were hedging their bets by giving alternative answers. Candidates should be deterred from this as an incorrect alternative will negate the mark as in this case. 0 mark given.

Results Plus: Examiner Tip Know the meanings of the hazard symbols. Avoid giving alternative answers as in this example as an incorrect answer will negate the mark.

Q2. No Examiner's Report available for this question Q3. No Examiner's Report available for this question

Q4.

Most candidates scored at least 1 mark but many did not answer the question instead describing what the symbols meant. Others were too vague when discussing precautions and answers such as 'wear protective equipment/clothing' frequently appeared which could not be credited.

Results Plus: Examiner Comments Answers such as this were unfortunately quite common. The candidate is trying to explain the meaning of the hazard symbols rather than suggesting safety precautions which the chemist should take.

Results Plus: Examiner Comments This was the most common way of scoring two marks.

Q5.

(b)(i)

The majority of candidates knew that argon can be used to put out fires because it is nonflammable.

(b)(ii)

The majority of candidates knew that helium is used in airships because it has a low density.

(c)(i)

It was disappointing that not many candidates knew the appearance of chlorine at room temperature. The appearance of bromine and iodine were given as a colour and a physical state and there were 2 marks for this question, so candidates should also have given the appearance

of chlorine as a colour and a physical state. A common incorrect answer was that chlorine is a blue liquid, showing that candidates were probably confused with the use of chlorine in swimming pools. Candidates would benefit from being shown a gas jar of chlorine.

Results Plus: Examiner Comments This candidate scored 1 mark for gas.

Results Plus: Examiner Tip If you are given some information in a question, try to see if there is a pattern and answer in a similar way. In this question, the appearances of bromine and iodine are described with a colour and a physical state. The appearance of chlorine should also include the colour and physical state.

Results Plus: Examiner Comments This is an example of an answer that scored 2 marks as it includes the correct colour and physical state for chlorine.

(c)(ii)

The majority of candidates could write the correct word equation.

Some candidates decided to attempt to write a balanced equation, but credit was only given if this was completely correct. Symbols such as H or Cl should not be used for hydrogen and

chlorine gas. Candidates are advised to write word equations when they are asked to do so in a question.

Some candidates also lost marks by writing CL as the symbol for chlorine and others changed the product to hydrochloric acid, hydrochloride or hydrogen chlorine.

Results Plus: Examiner Comments This answer scores 1 mark for hydrogen + chlorine. The candidate has written the name of the product as hydrogen chlorine, which is incorrect.

Results Plus: Examiner Tip Copy the names of chemicals carefully from the question.

Results Plus: Examiner Comments This candidate tried to write a balanced equation, but the formulae are incorrect so no marks were given.

Results Plus: Examiner Tip If a question asks for a word equation, do not try to write a balanced equation.

Results Plus: Examiner Comments This is an example of a correct word equation, scoring 2 marks.

Q6.

This was very well-answered by the majority of candidates. Most were able to recall the correct formulae for the reactants and products, with fewer gaining the balancing mark.

A common error often related to not writing the formula for oxygen correctly, e.g. 'O' as opposed to 'O2', on the reactants side. Also, examiners noted that marks were lost due to careless use of lower and upper case letters for symbols or not correctly using subscripted numbers in formulae, e.g. the formula for carbon dioxide frequently shown incorrectly as 'Co2' or 'Co2' as opposed to CO2.

Results Plus: Examiner Comments A typical response which did not score, containing commonly seen errors. The formula for oxygen is incorrectly shown on the Left Hand Side. The Right Hand Side is incorrect since the symbol for the oxygen atom in the formula for carbon dioxide has been shown incorrectly as lower case letter. The balancing is incorrect since it is consequential of the correct formulae.

Results Plus: Examiner Tip Be careful when writing out formulae, e.g. for carbon dioxide, CO2 but not Co2.

Results Plus: Examiner Comments This response scored 1 mark only. The products are correctly written on the Right hand Side, however, the formulae for oxygen on the Left hand Side is incorrect, since it has been shown as 'O' and not 'O2'. The balancing mark is not scored, since this mark is consequential of the correct formulae having been shown.

Q7.

Nearly half of the candidates could write the correct balanced equation given the information in the question; a further one third scored one mark for a partly correct word equation. It was disappointing to see that so many could not copy the reactants correctly; 'calcium solution' and 'sodium solution' were commonly seen as reactants. Many candidates used just the information and formed the products 'calcium carbonate + salt' or more frequently 'calcium carbonate + another salt'. A small number thought they had to write a balanced equation and invariably failed as they were making up formulae for the substances, e.g. SC for sodium carbonate. Candidates

should be advised that where a word equation is asked for, they are not expected to write a balanced equation using chemical formulae.

Results Plus: Examiner Comments Quite a common answer. However, 1 mark was score for the correct reactants.

Results Plus: Examiner Comments All the correct substances, but in the wrong places. This scored 0 marks.

Results Plus: Examiner Comments Here is an attempt to write a balanced equation using invented chemical formulae. Answers like this can only be awarded 0 marks.

Results Plus: Examiner Tip When word equations are asked for, do not attempt to write a balanced equation using chemical formulae. Use the information in the question to help in the construction of the word equation.

Q8.

(a) This proved to be a good discriminator. Some weaker candidates did not attempt the question. Of those that did, many used the formulae which had been given in the question but some then didn't balance the equation correctly. Other candidates were far too inclined to change the formulae from the ones stated in the question, often by incorrect use of subscripts in the product such as stating H2Cl2

Results Plus: Examiner Comments This was awarded 1 mark for the correct formulae but did not gain the second mark as it was incorrectly balanced.

(b) Candidates generally scored 2 marks or no marks on this question indicating they either knew it well or not at all. Many did not attempt the question. Of those that did, many answers saw candidates trying to combine the two elements into one single, combined structure labelled HCl. Many still drew inner shells despite being told not to in the question but were still able to score both marks. Some thought the bonding was ionic and drew diagrams indicating electron transfer from hydrogen to chlorine. However it was pleasing to see some very well drawn fully correct answers.

Results Plus: Examiner Comments This type of answer was surprisingly common. The two atoms have been combined into one and labelled as one structure HCl.

Results Plus: Examiner Comments A well drawn fully correct answer.

Results Plus: Examiner Comments This answer gained one mark for the shared pair of electrons but unfortunately has the incorrect number of electrons in the outer shell of chlorine.

Q9.

Several candidates were able to interpret the information correctly and produce a correctly balanced equation. The commonest error was found to be that chlorine was not recognised as a diatomic molecule so giving 2Cl on left hand side; the resultant equation scored one mark. Balanced equations of this type will be tested on the F-tier paper where a simple ratio exists between the reactants and or products. The weaker candidates attempted a word equation, which did not score. Other errors included incorrect symbols such as 'BA', 'ba' and 'CL', but they were not present in significant numbers.

Other errors found included incorrect balancing which limited them to 1 mark. Other ways in which a mark could be scored and were seen included '2Ba + 2Cl → 2BaCl2 ',

'Ba2+ + Cl- → BaCl2'. Some correctly gave BaCl2 or Ba + Cl2 but didn't draw an arrow to show where in the equation these appeared and so could not be credited.

Results Plus: Examiner Comments The Ba2 did not score, so 1 mark was given for the correct right hand side of the equation.

Results Plus: Examiner Comments Correct formulae on both sides of the equation was spoilt by incorrect balancing of the equation. Only 1 mark was given.

Results Plus: Examiner Comments Word equations do not score when asked for balanced equations.

Results Plus: Examiner Comments This was probably the most frequent of the errors seen. These candidates had not realised that the formula of chlorine gas is Cl2. 1 mark was awarded.

Results Plus: Examiner Tip Use the information given when constructing balanced equations. You will be expected to know the formulae of simple compounds you have met in the course, for example, sodium hydroxide, water etc., and you should also know the formulae of the gaseous elements such as hydrogen (H2), oxygen (O2) and that they all have 2 atoms in one molecule. Spend time making sure you can balance simple equations.

Q10.

(i)

Most candidates gained credit for their answers, scoring the 1 mark available for simply stating 'gas'.

(ii)

Most candidates gained credit for their answers.

Results Plus: Examiner Comments This response was the most commonly seen correct answer for the 1 mark available.

Results Plus: Examiner Comments A typical incorrect answer, where the reversible sign was confused with simply an equal sign, so does not score.

Q11. No Examiner's Report available for this question

Mark Scheme Q1.

Answer Acceptable

answers Mark

(i) corrosive damages skin / (1)

clothes causes burns

(ii) C neutralisation (1)

Q2.

Q3.

Q4.

Q5.

Q6.

Q7.

Answer Acceptable

answers Mark

sodium carbonate + calcium nitrate → sodium nitrate + calcium carbonate (2) LHS (1) RHS (1)

ignore solution / state symbols ignore incorrect attempts at balanced equation ignore mixtures of words and formulae (2)

Q8.

Q9.

Answer Acceptable

answers Mark

Ba + Cl2 (→) (1) → BaCl2 (1) reactants = 1 product = 1

max 1 for any incorrectly balanced equation

(2)

Q10.

Answer Acceptable

answers Mark

(i) gas ignore g alone (1)

(ii) reaction is reversible / reaction goes both ways

reaction is in /reaches equilibrium

(1)

Q11.