Find the molecular formulae for the compound given below. A r : H = 1 , C = 12 , N = 14 , O = 16 Compound M r Empirical formula Molecular formula Glucose 180 CH 2 O

Formula mass of glucose CH 2 O n = n 12 u + 2 × 1 u + 16 u = 30 n u ⇒ 30 n u = 180 u ⇒ n = 180 u 30 u = 6 Hence, the molecular formula for glucose is CH 2 O 6 = C 6 H 12 O 6

Mercury (lI) oxide breaks down on heating: A r : O = 16 , Hg = 201 2 HgO ( s ) → 2 Hg ( l ) + O 2 ( g ) Calculate the mass of 1 mole of mercury (ll) oxide.

The mass of one mole of any substance is referred to as molar mass which is equal to its molecular mass expressed in gram. The molecular formula for mercury (II) oxide is HgO its M r = 201 u + 16 u = 217 u Hence, the mass of one mole of mercury is 217 g .

Mercury (lI) oxide breaks down on heating: A r : O = 16 , Hg = 201 2 HgO ( s ) → 2 Hg ( l ) + O 2 ( g ) How much mercury and oxygen could be obtained from 21 . 7 g of mercury (ll) oxide? Only 19 . 0 g of mercury was collected. Calculate the % yield of mercury for this experiment.

2 HgO ( s ) → 2 Hg ( l ) + O 2 ( g ) Number of moles of mercury (II) oxide in its 21 . 7 g = 21 . 7 g 217 g = 0 . 1 mol From the reaction, it is clear that two moles of mercury (II) oxide produce two moles of mercury and one mole of oxygen gas. Therefore, 0 . 1 mol of mercury (II) oxide will produce 0 . 1 mol of mercury and 0 . 05 mol of oxygen gas. The mass of 0 . 1 mol of mercury is 20 . 1 g and the mass of 0 . 1 mol of oxygen gas is 1 . 6 g . Since only 19 . 0 g of mercury was collected. Therefore, the percent yield of mercury = 19 . 0 g 20 . 1 g × 100 = 94 . 5 %

A 5 g sample of impure magnesium carbonate is reacted with an excess of hydrochloric acid: MgCO 3 ( s ) + 2 HCl ( aq ) → MgCI 2 ( aq ) + H 2 O ( l ) + CO 2 ( g ) 1250 cm 3 of carbon dioxide is collected at rtp. How many moles of CO 2 are produced?

Since, the volume of carbon dioxide collected is 1250 Cm 3 = 1 . 25 dm 3 . Number of moles of CO 2 = 1 . 25 dm 3 24 dm 3 ≈ 0 . 052 mol

A 5 g sample of impure magnesium carbonate is reacted with an excess of hydrochloric acid: MgCO 3 ( s ) + 2 HCl ( aq ) → MgCI 2 ( aq ) + H 2 O ( l ) + CO 2 ( g ) 1250 cm 3 of carbon dioxide is collected at rtp. Calculate the % purity of the 5 g sample. A r : C = 12 , O = 16 , Mg = 24

1250 Cm 3 of carbon dioxide contains 0 . 052 mol . MgCO 3 ( s ) + 2 HCl ( aq ) → MgCI 2 ( aq ) + H 2 O ( l ) + CO 2 ( g ) From the reaction, it is clear that one mole of magnesium carbonate gives one mole of carbon dioxide. Hence, 0 . 052 mol or 1250 Cm 3 of carbon dioxide will be collected by 0 . 052 mol of magnesium carbonate. Mass of 0 . 052 mol of magnesium carbonate = 0 . 052 mol × 84 g = 4 . 368 g Percentage purity of magnesium carbonate sample is = 4 . 368 g 5 g × 100 ≈ 87 %

RoseMarie Gallagher and Paul Ingram Solutions for Chapter: Using Moles, Exercise 9: Checkup on Chapter 6

Author:RoseMarie Gallagher & Paul Ingram

RoseMarie Gallagher Chemistry Solutions for Exercise - RoseMarie Gallagher and Paul Ingram Solutions for Chapter: Using Moles, Exercise 9: Checkup on Chapter 6

Attempt the free practice questions on Chapter 6: Using Moles, Exercise 9: Checkup on Chapter 6 with hints and solutions to strengthen your understanding. Complete Chemistry for Cambridge IGCSE® Second Edition solutions are prepared by Experienced Embibe Experts.

Questions from RoseMarie Gallagher and Paul Ingram Solutions for Chapter: Using Moles, Exercise 9: Checkup on Chapter 6 with Hints & Solutions

MEDIUM

Upper Secondary: IGCSE

IMPORTANT

Complete Chemistry for Cambridge IGCSE® Second Edition>Chapter 6 - Using Moles>Checkup on Chapter 6>Q 11

Find the molecular formulae for the compound given below. $[A_{r} : H = 1, C = 12, N = 14, O = 16]$

Compound	$M_{r}$	Empirical formula	Molecular formula
Glucose	$180$	${CH}_{2} O$

EASY

Upper Secondary: IGCSE

IMPORTANT

Complete Chemistry for Cambridge IGCSE® Second Edition>Chapter 6 - Using Moles>Checkup on Chapter 6>Q 12

Hydrocarbons A and B both contain $85.7 %$ carbon. Their molar masses are $42 g$ and $84 g$ respectively. Which elements does a hydrocarbon contain?

MEDIUM

Upper Secondary: IGCSE

IMPORTANT

Complete Chemistry for Cambridge IGCSE® Second Edition>Chapter 6 - Using Moles>Checkup on Chapter 6>Q 12

Hydrocarbons A and B both contain $85.7 %$ carbon. Their molar masses are $42 g$ and $84 g$ respectively. Calculate the empirical formulae and molecular formulae of A and B.

EASY

Upper Secondary: IGCSE

IMPORTANT

Complete Chemistry for Cambridge IGCSE® Second Edition>Chapter 6 - Using Moles>Checkup on Chapter 6>Q 13

Mercury (lI) oxide breaks down on heating: $[A_{r} : O = 16, Hg = 201]$

$2 HgO (s) \to 2 Hg (l) + O_{2} (g)$

Calculate the mass of $1$ mole of mercury (ll) oxide.

HARD

Upper Secondary: IGCSE

IMPORTANT

Complete Chemistry for Cambridge IGCSE® Second Edition>Chapter 6 - Using Moles>Checkup on Chapter 6>Q 13

Mercury (lI) oxide breaks down on heating: $[A_{r} : O = 16, Hg = 201]$

$2 HgO (s) \to 2 Hg (l) + O_{2} (g)$

How much mercury and oxygen could be obtained from $21.7 g$ of mercury (ll) oxide?
Only $19.0 g$ of mercury was collected. Calculate the $%$ yield of mercury for this experiment.

EASY

Upper Secondary: IGCSE

IMPORTANT

Complete Chemistry for Cambridge IGCSE® Second Edition>Chapter 6 - Using Moles>Checkup on Chapter 6>Q 14

A $5 g$ sample of impure magnesium carbonate is reacted with an excess of hydrochloric acid:

${MgCO}_{3} (s) + 2 HCl (aq) \to {MgCI}_{2} (aq) + H_{2} O (l) + {CO}_{2} (g)$

$1250 {cm}^{3}$ of carbon dioxide is collected at rtp. How many moles of ${CO}_{2}$ are produced?

MEDIUM

Upper Secondary: IGCSE

IMPORTANT

Complete Chemistry for Cambridge IGCSE® Second Edition>Chapter 6 - Using Moles>Checkup on Chapter 6>Q 14

A $5 g$ sample of impure magnesium carbonate is reacted with an excess of hydrochloric acid:

${MgCO}_{3} (s) + 2 HCl (aq) \to {MgCI}_{2} (aq) + H_{2} O (l) + {CO}_{2} (g)$

$1250 {cm}^{3}$ of carbon dioxide is collected at rtp. What mass of pure magnesium carbonate would give this volume of carbon dioxide? $[A_{r} : C = 12, O = 16, Mg = 24]$

HARD

Upper Secondary: IGCSE

IMPORTANT

Complete Chemistry for Cambridge IGCSE® Second Edition>Chapter 6 - Using Moles>Checkup on Chapter 6>Q 14

A $5 g$ sample of impure magnesium carbonate is reacted with an excess of hydrochloric acid:

${MgCO}_{3} (s) + 2 HCl (aq) \to {MgCI}_{2} (aq) + H_{2} O (l) + {CO}_{2} (g)$

$1250 {cm}^{3}$ of carbon dioxide is collected at rtp. Calculate the $%$ purity of the $5 g$ sample. $[A_{r} : C = 12, O = 16, Mg = 24]$

RoseMarie Gallagher and Paul Ingram Solutions for Chapter: Using Moles, Exercise 9: Checkup on Chapter 6

RoseMarie Gallagher Chemistry Solutions for Exercise - RoseMarie Gallagher and Paul Ingram Solutions for Chapter: Using Moles, Exercise 9: Checkup on Chapter 6

Questions from RoseMarie Gallagher and Paul Ingram Solutions for Chapter: Using Moles, Exercise 9: Checkup on Chapter 6 with Hints & Solutions

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