Exercise Chap3 Form 4

http://chemclass4spm.blogspot.com http://chemclass4spm.blogspot.com Exexcise : Relative Atomic Mass and Molecular Mass Relative atomic mass is given in exam. Relative Molecular Mass (RMM) is obtained by adding up the relative atomic mass of all atoms that are present in the molecule. For ionic substances, RMM is replaced with RFM (Relative Formula Mass) 1. A platinum atom is five times heavier than a potassium atom. What is the relative atomic mass of platinum? [RAM K, 39] 5 x 39 = 195 2. Five aluminium atoms have same mass as the sum of six lithium atoms and three phosphorus atoms. Determine the relative atomic mass of Phosphorus. [RAM Li, 7; Al, 27] 5Al = 6Li + 3P 5 x 27 = 6 x 7 + 3P P = 31 3. The mass of a rutherfordium (Rf) atom is equal to the sum of three sodium atoms and six sulphur atoms. What is the relative atomic mass of Rf. [A r : Na, 23 ; S, 32] Rf = 3Na + 6S Rf = (3 x 23) + (6 x 32) = 261 4. Adrenaline is produced by adrenal gland. Adrenaline has the formula C 9 H 13 NO x . If its relative molecular mass is 183, determine the value of x. 9C + 13H + 1N + xO = 183 (9x12) + (1x13) + (1x14) + 16x = 183 x = 3 5. The relative formula mass of a compound with formula Y 2 SO 4 is 142. Calculate the relative atomic mass of element Y. [A r :O, 16; S, 32] 2Y + 1S + 4O = 142 2Y + 32 + (4x16) = 142 Y = 23 6. Iridium is a very dense metal and was discovered in 1804. Determine how many carbon atoms will have the same mass as one iridium atom. [A r : C, 12 ; Ir, 192] xC = 192 12x = 192, x = 16 7. How many magnesium atoms will have the same mass as two silver atoms? [A r : Mg, 24; Ag, 108] xMg = 2Ag 24x = 2 x 10 8. The relative atomic mass of elements W, X, Y and Z are 7, 39, 56 and 195 respectively. i. One atom of Thorium (Th) has the same mass as the sum of six W atoms, two X atoms and two Y atoms. What is the relative atomic mass of Th atom? 1Th = 6W + 2X + 2 Y 1Th = 6 x 7 + 2 x 39 + 2 x56 Th = 232 ii. How many W atoms will have the same mass as the sum of two X atoms, one Y atom and one Z atom. nW = 2X + 1Y + 1Z 7n = 2x39 + 56 + 195 n = 47 9. The relative atomic mass of elements X, Y and Z are 12, 16 and 24 respectively. i. How much is an atom of Z heavier than atom of X? 24 ÷ 12 = 2 times ii. How many atoms of X will have the same mass as the sum of 3 atoms of Y and 2 atoms of Z? nX = 3Y + 2Z 12n = 3 x 16 + 2 x 24 n = 8 10. Borax is a compound used to kill cockroaches. Its molecular formula is X 2 B 4 O 7 . If the relative molecular mass of borax is 202, determine the relative atomic mass of the element X. Identify the element X from the list of elements given below. [A r : B, 11; C, 12; O, 16; F, 19; Na, 23; Mg, 24] 2X + 4B + 7O = 202 2X + (4x11) + (7x16) = 202 X = 23 X is a Na, Sodium.

Exercise Chap3 Form 4

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