Quantitative Chemistry

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Question 1What is the mass in grams of one molecule of

ethanoic acid CH3COOH?

0.1 1 x 10-22

603.6 x 1025

Wrong Answer!Molar mass of CH3COOH is 24 + 4 + 32 = 60

Question 2

Which is not a true statement?

One mole of methane contains four moles of hydrogen atoms.

One mole of 12C has a mass of 12.00g.

One mole of methane contains 75% of carbon by mass.

One mole of hydrogen gas contains 6.02 x 1023 atoms of hydrogen.

Wrong Answer!1 mole of hydrogen gas contain 6 x 1023 molecules of hydrogen gas. Since 1 mole of hydrogen is made up of 2 H atoms, 1 mole of hydrogen gas contains 2 x 6 x 1023 atoms.

Question 3

Which sample has the greatest mass?

1.0 mol N2H4 2.0 mol N2

25.0 mol H23.0 mol NH3

Wrong Answer!A: 1 x (28+4) = 32g

B: 2 x 28 = 56g

C: 3 x (14+3) = 51g

D: 25 x 2 = 50g

I only

Question 4Which one of the following statements about SO2

is/are correct?

I. One mole of SO2 contains 1.8 x 1024 atoms

II.One mole of SO2 has a mass of 64g

Both I and II Neither I nor II

II only

Wrong Answer!SO2 is made up of 3 atoms, hence 1 mole of SO2

contains 3 x 6 x 1023 atoms.

Molar mass of SO2 = 32 + 32 = 64.

two chloride ions

Question 5

2Cl2 represents:

two chlorine molecules two chlorine atoms

four free chlorine atoms

Wrong Answer!2Cl2 represents two chlorine molecules : Cl-Cl and Cl-Cl

Question 6

Which one of the following equations is not correctly balanced?

Ca(s)+2H+(aq)Ca 2+(aq)+H2

(g)

Mg(s)+ H2O(l)Mg(OH)2

(aq)+H2(g)

Fe 2+(aq)+ Cl2 (g) Fe3+(aq)+ 2Cl-(aq)

Fe 2+(aq)+Ag+(aq)Fe3+(aq)+ 2Cl-(aq)

Wrong Answer!The charge is not balanced.

Question 7Sulfuric acid and sodium hydroxide react together

according to the equation?

H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l)

What volume of 0.250 moldm-3 NaOH is required to neutralise exactly 25.0 cm3 of 0.125 moldm-3 H2SO4 ?

6.25 cm3 50 cm3

25.0 cm312.5 cm3

Wrong Answer!Conc x Vol of NaOH = 2 x Conc x Vol of H2SO4

0.25 x Vol of NaOH = 2 x 0.125 x 25

Vol of NaOH = 25 cm3

Question 8

Which expression represents the density of a gas sample of relative molar mass, Mr, at temperature T, and pressure, P?

rPM

RTrRM

PT

r

RT

PMrPM

T

Wrong Answer!

Density =

r

r

r

nRT PV

m PV

M RT

PMm

V RTPM

RT

Question 9Separate samples of two gases, each containing a

pure substance, are found to have the same density under the same conditions of temperature and pressure. Which statement about these two samples must be correct?

They have the same volume.

There are equal numbers of moles in the two samples.

They condense at the same temperature.

They have the same relative molecular mass.

Wrong Answer!

Density =

r

r

r

nRT PV

m PV

M RT

PMm

V RTPM

RT

Under the same pressure and temperature where R is a constant, they should have the same relative molecular mass.

Question 10A 250 cm3 sample of an unknown gas has a mass

of 1.42g at 350C and 0.85 atmospheres. Which expression gives its molar mass, Mr? (R = 82.05 cm3 atm K-1 mol-1)

1.41 82.05 308

250 0.85

1.41 82.05 35

0.25 0.85

1.41 82.05 308

0.25 0.85

1.41 250 0.85

82.05 308

Wrong Answer!

r

r

nRT PV

massRT PV

M

massRTM

PV

Question 11

What is the concentration of nitrate ions in 0.500cm3 of 0.60moldm-3 Fe(NO3)3 solution?

0.60 moldm-3 0.90 moldm-3

1.80 moldm-3 1.20 moldm-3

Wrong Answer!Fe(NO3)3 Fe3+(aq) + 3NO3

-(aq)

Nitrate ions concentration = (0.6 x 3) = 1.80 moldm-3

Question 12

32.0 grams of sulfur (atomic mass of 32.0) combine with a metal, M (atomic mass of 40.0) to give a product which weighs 52.0g. What is the empirical formula of the sulfide formed?

MS MS2

M2S5M2S

Wrong Answer!Amount of M atoms = (52-32)/40 = 0.50 mol

Amount of S atoms = 32/32 = 1.0 mol

Multiplying through by 2 gives MS2

Question 13Under what conditions of temperature and pressure will a real gas

behave most like an ideal gas?

Temperature Pressure

Low Low

Low High

High Low

High High

Wrong Answer!High pressure will bring the gas molecules very close together. This causes more collisions and also allows the weaker attractive forces to operate. With low temperatures, the gas molecules do not have enough kinetic energy to continue on their path to avoid the attraction.

39 gmol-1

Question 14

At stp (i.e. 00C and 1 atm pressure (101 kPa)), it was found that 1.15 dm3 of a gas weighed 3.96g. What is its molar mass?

77 gmol-1 47 gmol-1

4 gmol-1

Wrong Answer!

3 3

1 1

1

101000 1.15 100.0512

8.31 2733.96g

Molar mass = 77.340.0512mol

PV Pa mn mol

RT Jmol K K

gmol

Question 15

A sample of argon gas in a sealed container of fixed value is heated from 50 to 2500C. Which quantity will remain constant?

Average speed of the atoms

Pressure of the gas

Density of the argonAverage kinetic energy of the atoms

Wrong Answer!All properties will increase in value except density which remain constant since the mass and volume of gas remain constant.

Question 16Nitrogen(II) oxide,NO, is made from the oxidation of NH3:

4NH3 + 5O2 4NO + 6H2O

An 8.5g sample of NH3 gives 15.0g of NO. What is the percentage yield of NO?

40% 60%

100%80%

Wrong Answer!Amount of NH3 = 8.5/17 = 0.5 mol

Amount of NO = 15/30 = 0.5 mol

Percentage yield = 0.5/0.5 x 100% = 100%

Question 17A pure compound contains 24g of carbon, 4g of

hydrogen and 32g of oxygen. No other elements are present. What is the empirical formula of the compound?

C2H4O2 CH2O

CHOCH4O

Wrong Answer!No. of moles of C = 24/12 = 2

No. of moles of H = 4/1 = 4

No. of moles of O = 32/16 = 2

Dividing all by 2 gives a ratio of C:H:O = 1:2:1

The empircal formula is CH2O

Question 181000cm3 of ammonia gas combines with 1250cm3 of

oxygen to produce two gaseous compounds with a combined volume of 2500cm3, all volumes being measured at 2000C and 0.500 atm pressure. Which of the following equations fits the facts?

4NH3 + 7O2 4NO2 + 6H2O

4NH3 + 5O2 4NO + 6H2O

4NH3 + 3O2 2N2+ 6H2O

4NH3 + 5O2 4N2O2 + 6H2O

Wrong Answer!4 vol + 5 vol 10 vol

Experimental data 1 vol + 1.25 vol 2.5 mol

Multiplying throughout by 4 gives 4 vol + 5 vol 10 vol

Question 19Butane burns in oxygen according to the equation

2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g)

If 11.6g of butane is burned in 11.6g of oxygen which is the limiting reagent?

Neither Butane

Oxygen and butaneOxygen

Wrong Answer!No. of moles of butane = 11.6/58 = 0.2

No. of moles of oxygen = 11.6/32 = 0.3625

2 mols of butane react with 13 mols of oxygen

0.2 mols of butane will react with 1.3 mols of oxygen.

0.3625 mols of oxygen will react with 0.05577 mols butane.

The limiting reagent is oxygen since the no. of mols of butane produced by 0.3625 mols is smaller.

Question 20

A 350cm3 sample of helium gas is collected at 22.00C and 99.3kPa. What volume would this gas occupy?

318cm3 450cm3

220cm3477cm3

Wrong Answer!3

2

3 32

350 99.3 273

101.3 295

317.5034 318

cm kPa KV

kPa K

V cm cm

Question 21When 250 cm3 of 3.00 moldm-3 HCl(aq) is added to

350 cm3 of 2.00 moldm-3 HCl(aq) the concentration of the solution of hydrochloric acid obtained in moldm-3 is:

1.45 2.90

2.422.50

Wrong Answer!(250+350)/1000 x Conc of HCl

= 250/1000 x 3 + 350/1000 x 2

Conc of HCl = (0.25 x 3 + 0.35 x 2)/0.6 = 2.416moldm-3

Question 22

Magnesium reacts with hydrochloric acid according to the following equation:

Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

What mass of hydrogen will be obtained if 100 cm3

of 2.00 moldm-3 HCl are added to 4.86g of magnesium?

2.0g 0.8g

0.2g0.4g

Wrong Answer!No. of moles of HCl = 100/1000 x 2 = 0.2

No. of moles of Mg = 4.86/24 = 0.2025

The limiting reagent is HCl

Since 2 mols of HCl produces 1 mol H2, 0.2 mols of HCl produces 0.1 mol H2. Hence, 0.1 x 2g = 0.2g of H2

Question 2312g of anhydrous magnesium sulfate combines

with 12.6g of water to form hydrated manesium sulfate. What is the formula of the hydrated magnesium sulfate?

MgSO4.9H2O MgSO4.7H2O

MgSO4.3H2OMgSO4.5H2O

Wrong Answer!No. of moles of MgSO4 = 12/122 = 0.09836

No. of moles of H2O = 12.6/18 = 0.7

Multiplying by 10 to both gives approximately

1 mole MgSO4 and 7 moles H2O

Question 24

In order to dilute 40.0 cm3 of 0.600 moldm-3 HCl(aq) to 0.100 moldm-3, what volume of water must be added?

60 cm3 160 cm3

240 cm3 200 cm3

Wrong Answer!M1V1= M2V2

0.600moldm-3 x 40.0cm3 = 0.600moldm-3 x V2

V2 = 240cm3

V2 – V1 = 240 – 40 = 200 cm3

Congratulations!