Calculations LBL2

8/10/2019 Calculations LBL2

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1. Define the following:

a) mass,

b) volume,

c) amount,d) concentration,

e) dilution.

Give examples of typical units used to describe each of the above.

Answer:

he units of measurement in current use are those of the !ysteme "nternational

d#$nites %!"), 1&'(.

a) ass can be defined as a measure of how much matter is in an ob*ect. ass ismeasured in +ilogrammes %+g).

b) A measurement of the amount of space contained within a threedimensional

shape. -olumes in the laboratory are measured in litres or parts of a litre litre

is not an !" $nit but a metric unit. he !" unit for volume is cubic metres

%m/).

c) he amount of a substance that contains as many elementary units as there are

atoms in (.(10 +g of carbon10. he !" unit for amount of substance is moles

%mol).

d) he concentration of a solution is expressed as the amount of solute in a given

volume of liuid

2oncentration 3 4umber of moles

-olume of solvent %5)

3 mol65

7e can express concentration as mass per volume e.g. 0( grams6 litre. 7e can

also express concentration in terms of moles per litre. here are three different

ways of writing this, either (.1 moles6litre or (.1 mol51 or (.1. he 8#stands for molar.

e) 9rocess of reducing the concentration of a solute in solution, usually simply by

mixing with more solvent.

ou can calculate the concentration of a solution following a dilution by

applying this euation:

i-i 3 f-f

7here is molarity, - is volume, and the subscripts i and f refer to the initial

and final values.

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=xample:

>ow many millilitres of ?.? 4a@> are needed to prepare /(( m5 of 1.0

4a@>

!olution:

?.? x -1 3 1.0 x (./ 5-1 3 1.0 x (./ 5 6 ?.?

-1 3 (.('? 5

-1 3 '? m5

!o, to prepare the 1.0 4a@> solution, you pour '? m5 of ?.? 4a@> into

your container and add water to get /(( m5 final volume.

0. 4ame and define the correct !" unit for each of the following:

a) amount,

b) volume,c) time,

d) en;yme activity.

Answer:

a) he !" unit for amount of substance is moles %mol). A mole is defined as the

amount of substance that contains as many elementary particles %atoms, ions,

molecules) as there are in 10g of carbon10 atoms.

b) he !" unit for volume is cubic metres %m/). "t is defined as a volume that is

made by a cube that is 1 meter on each side. "t is eual to 1((( %one thousand)

litres.

c) he second is the basic unit of time. he time ta+en for &,1&0,'/1,BB( periods

of vibration of the caesium1//atom to occur.

d) he !" unit is the +atal and is used to measure total units of activity in a given

volume of solution.

1 +atal 3 1 mol sC1

atal, however is an excessively large unit. A more practical and commonlyused value is 1 en;yme unit %$) 3 1 Emol minC1. 1 $ corresponds to

1'.'B nano+atals.

/. 7riting the answers in both decimal form and in standard form:

a) =xpress F.< mmol as %i) mol %ii) nmol and %iii) mol

b) =xpress 0B.' 5 as %i) m5 and %ii) li tres

Answer:

a) F.< mmol

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i) F.


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c) Ieporting your answer to / significant figures, what will the final

concentration of urea be if 1.0? m5 of stoc+ solution is mixed with

0.?( m5 water

Answers:

a)

2oncentration ( mmol65 ? mmol65 1?

mmol65

0(

mmol65

/?

mmol65

-olume of stoc+

standard %m5)

( (.? 1.? 0 /.?

-olume of water

%m5)

?


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$sing the euation

i-i3f-f

?(mmol65 x 1.0?m5 3 f x 0.?( m5

f3 ?(mmol65 x 1.0?m560.?(m5f3 0?mmol65

Jinal concentration of urea 3 0?mmol65 or 0?( x 1(H1 mmol65

?. 2onvert (.0F0? g65 creatinine solution to molar, millimolar and

micromolar concentrations. %creatinine has the molecular formula

2B4/@)

Answer:

olar ass of 2reatinine3 11/.10

Amount %in moles) 3 Amount %in g) 6 olar ass %g.mol1)

3 (.0F0?g 6 11/.10 g.mol1

3 (.((0? mol

2oncentration %) 3 Amount %in mol) 6 -olume %in 5)

3 (.((0?mol615

2oncentration %) 3 (.((0?

@r in millimolar

2oncentration %) 3 (.((0? x 1(H/m6

3 0.?m

or in micromolar

2oncentration %) 3 (.((0? x 1(H'6

3 0?(( or 0.? x 1(H/

'. A urine sample that has tested positive for blood using a dipstic+

reuires red and white blood cell counts to be underta+en. he number

of cells is counted in a three separate haemocytometer grids of

dimensions 1 mm x (.0 mm x (.< mm. 2alculate the number of red and

white blood cells per microlitre, per millilitre and per litre of the patient

sample from the following grid counts.

a) Ied blood cell counts: 0/, 1&, 0?b) 7hite blood cell counts: F, &, 11

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Answer:

a) Ied 2ell 2ounts

i. 2alculate average of the counts %0/K1&K0?)6/ 3 00.//ii. he volume of the suare of the counting chamber in which the cells

were counted is 1x(.0x(.


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a) 7hat data is missing from the above

b) 7hat limits the usefulness of the information above

c) 9lot a line graph to represent the above data using icrosoft =xcel,

ensure full labelling.

d) 9lot a bar chart of the mean number of samples from each G9 surgeryusing icrosoft =xcel.

Answer:

a) 7hat data is missing from the above

here is no data regarding number of staff during the laboratory wor+ing

hours.

b) 7hat limits the usefulness of the information above

Mecause there is no data regarding staffing levels in the laboratory during its

wor+ing hours, the above data limits its usefulness to address the pea+ times in

the laboratory.

c) 9lot a line graph to represent the above data using icrosoft =xcel, ensure full

labelling.

d) 9lot a bar chart of the mean number of samples from each G9 surgery using

icrosoft =xcel.

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Calculations LBL2

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