Test 1 (2020 CV) Answers Reactions calcs exo endo copy PDF

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FACULTY OF SCIENCE

ATAR CHEMISTRY Reactions, Equations, Energy Changes TEST #1 (CV), 2020.

Name of Student:

ANSWERS MULTIPLE CHOICE QUESTION BOOKLET

1

Section A - Multiple choice

(10 marks)

Answer the multiple choice questions on the answer sheet provided on page. The following information refers to questions 1 and 2. Examine the following potential energy diagram for a chemical reaction:

1 The enthalpy change ∆H and the activation energy Ea in kJ for the reaction are respectively A B C D

∆H ∆H ∆H ∆H

2

If a catalyst is added to the system

A B C D

both H and Ea decrease ∆H remains constant but Ea decreases ∆H decreases and Ea remains constant both ∆H and Ea remain constant.

3

A student adds a chemical to water and stirs it with a thermometer until it has dissolved. She correctly deduces that it is endothermic. What observation could she have made to deduce this?

A B C D 2

= = = =

–25 kJ +25 kJ 35 kJ –60 kJ

and and and and

Ea = 35 kJ Ea = 35 kJ Ea = 60 kJ Ea = 35 kJ

The chemical dissolved (it would not dissolve if it were exothermic). The temperature did not change, hence energy is required to be added. The temperature of the solution was lower than the initial temperature of the water. The temperature of the solution was higher than the initial temperature of the water.

3

4

Barium nitrate and barium chloride were mixed in water to form a solution X. Sodium carbonate and potassium chloride were mixed in water to form a solution Y. When X and Y were mixed, a white precipitate was formed. What is this white precipitate?

A B C D

barium sulfate barium carbonate sodium chloride potassium carbonate.

5

Which of the following is not an example of an exothermic reaction?

A

Melting ice Lighting a match Burning a strip of Magnesium ribbon in oxygen gas Steel wool reacting with copper sulfate solution

B C D

6

Approximately equal volumes of the two solutions in the following pairs of solutions listed below are mixed together. All solutions are 0.1 mol L-1 I

Pb(NO3)2(aq)

and

Na2CO3(aq)

II

MgCl2(aq)

and

(NH4)2SO4(aq)

III

BaCl2(aq)

and

Na2SO4(aq)

IV

NH4NO3(aq)

and

KCl(aq)

V

NaCl(aq)

and

AgNO3(aq)

A precipitate will form in: A B C D

7

A B C D 4

I and IV only. II and III only. I, II and III only. I, III and V only.

How many feathers are there in 2 moles of feathers?

6.022 × 1023 1.204 × 1024 Need to know average mass of feathers 3.022 × 1023

8

What is required to calculate the percentage composition of a substance?

A

Chemical formula and relative atomic masses of the elements in the compound

B C D

Chemical formula only Chemical formula and relative mass of the compound Relative mass of the compound only

9

How many moles of oxygen are in 0.15 mol Al2(SO4)3?

A

0.3 mol

B C D

0.15 mol 0.6 mol 1.8 mol

(12 x 0.15 = 1.8 mol)

10 At which stage or stages was the reaction rate the fastest? a) 0 seconds b) 0–1 seconds c) d)

5

1–2 seconds 6–8 seconds

FACULTY OF SCIENCE ATAR CHEMISTRY Reactions, Equations, Energy Changes TEST #1 (CV), 2020.

Name of Student:

INSTRUCTIONS:

ANSWERS Write in blue or black pen. Please do not use red pen.

Multiple Choice Questions  Answer the multiple choice questions on the answer sheet provided. Shade in the box of the correct answer.

Short Answer Questions  

Answer all short answer questions in the spaces provided. Where appropriate, answer in full sentences.

Calculations  Show full working  Include equations where appropriate.  Answers should be given to the appropriate number of significant figures.

SECTION Multiple Choice Short Answer/Calculations Total

POSSIBLE MARK 10 39 49

MULTIPLE CHOICE ANSWER GRID 6

ACHIEVED MARK

(10 marks)

Shade in the box of the correct answer.

Short Answer

(35 marks)

Question 11

(2 marks)

Write balanced molecular equations for the following reaction: Include state symbols. Aluminium metal is heated with water vapour to give hydrogen gas and solid aluminium oxide. 2 Al (s) + 3 H2O (g)  3 H2 (g) + Al2O3(s)

Question 12

(6 marks)

Write balanced molecular and ionic equations. If no reaction occurs, write “no reaction”. In each case describe in full what you would observe, including any colours, odours, precipitates (give the colour) and gases evolved (give the colour or describe as colourless). No state symbols required. a)

Lead (II) nitrate solution is added to a solution of sodium iodide

[3]

molecular equation Pb(NO3)2 (aq) + 2 NaI (aq)  PbI2(s) + 2 NaNO3 (aq) ionic equation Pb2+ (aq) + 2 I - (aq)  PbI2(s) Observations __2 colourless solutions combine to form a yellow Precipitate in a colourless solution

7

b)

solid zinc carbonate is added to hydrochloric acid solution

[3]

molecular equation ZnCO3 (s) + 2 HCl (aq)  ZnCl2(aq) + CO2 (g) + H2O (l) ionic equation ZnCO3 (s) + 2 H+ (aq)  Zn2+ (aq) + CO2 (g) + H2O (l) Observations A white solid is added to a colourless liquid to produce bubbles of colourless, odourless gas in a colourless solution. The solid disappears. Question 13

[4]

Write a chemical equation which is consistent with the observation in each of the following experiments. What is done A green solution is

Observations A green precipitate

added to a

forms.

Equation Ni(NO3)2 (aq) + Na2CO3 (aq)  NiCO3(s) + 2 NaNO3 (or any reasonable reaction for 2 marks)

colourless solution. A silver grey metal is

A bright white light is

combusted in

seen.

2Mg(s) + O2 (g)  2 MgO (s)

2 marks

excess oxygen.

Question 14 Determine the percentage composition of each element in iron (II) sulfate. [2] %O = 4 x M(O) / M(FeSO4) x 100 = 4 x 16.00 / (55.85 + 32.07 + 4x 16.00) x 100 %O = 64.00 / 151.92 = 42.13 % = 42.1% (3sf)

8

Question 15

(3 marks)

Respiration can be represented by the following equation C6H12O6 + 6 O2

a)



6 CO2 + 6 H2O + energy

Calculate the molecular mass of glucose.

M(C6H12O6)

[1]

= 6 x 12.01 + 12 x 1.008 + 6 x 16.00 = 180.156 g/mol

b

How many moles of carbon dioxide are produced per mole of glucose? [1]

n(CO2) =

6 x n(C6H12O6) 1

answer: 6 moles c

How many molecules of water are produced per mole of oxygen consumed? [1]

n(H2O) = 6/6 x n(O2) = 1 mole of water x Av number = 1 x 6.022 x 1023 molecules of water _____________________________________________________________________________

9

Question 16

(6 marks)

Hydrogen sulfide gas reacts with excess oxygen gas to form sulfur dioxide gas and water according to the equation: ____2_ H2S + ____3 O2



_____2_ SO2 + _____2_ H2O

a) Balance the equation by writing the correct coefficients in the spaces above.

[1]

b) Calculate the mass of sulfur dioxide produced from 1.00 kg of hydrogen sulfide.

[2]

n( H 2

mass( H 2 S) 1000 = =29.34 mol M ( H 2 S) (2 x 1.008+32.07)

S) =

2 x n(H 2 S) = 2

n( S O 2 ) =

Mass (S O 2 )

29.34 mol (S O 2 )

= nM

= 29.34 x (32.07 + 2 x 16.00) = 1879.8 g (1880 g at 3 sf) or 1.88 kg (3 sf)

c) Calculate the mass of oxygen that is required for the complete combustion of the 1.0 kg of hydrogen sulphide? [3] n( O 2 ) =

3 x n (H 2 S) 2

Mass ( O 2 )

3 = 2 x 29.33=43.995 mol ( O 2 )

= nM = 43.995 x 2 x 16.00 = 1407.84 g required ~ 1410 g required (3sf)

10

Question 17

(4 marks)

Booster rockets used to launch the Space Shuttle burn a solid fuel composed of a mixture of aluminium and ammonium perchlorate as a propellant. The chemicals used in the fuel react according to the equation shown below. 3 A(s) + 3 NH4CO4(s) → A2O3(s) + AC3(s) + 3 NO(g) + 6H2O(g) 219 g A sample of this rocket fuel was tested, and after ignition 219 g of Al2O3(s) was produced. (a) What mass of ammonium perchlorate (NH4CO4) would have been used in the reaction? n(A2O3)

mass( A 2O 3) 219 219 = = =2.1479 mol M ( A 2O 3) (2 x 26.98+3 x 16.00) 101.96

=

n(NH4CO4) =

3 x n (A 2O 3) 1

= 3 x 2.1479 = 6.4437 mol

Mass (NH4CO4) = nM = 6.4437 x ( 14.01 + 4 x 1.008 + 35.45 + 4 x 16.00) = 6.4437 x (117.492) = 757.08 ~ 757 g (3 sf) Question 18 (8 marks) Sodium thiosulfate solution (Na2S2O3) reacts slowly with dilute hydrochloric acid to form a precipitate. The rate of this reaction can be studied by measuring the time (t) that it takes for a small fixed amount of precipitate to form under different conditions. The fixed amount of precipitate is taken as the amount needed to obscure a cross on paper. The equation for this reaction is shown below. Na2S2O3 + 2HCl →2NaCl + S + SO2 + H2O a)

Identify the insoluble product of this reaction which forms the precipitate. Any of the following:

b)

(i)

Sulfur S

S8 Sulphur

When this reaction takes place, the collision between the reacting particle requires an activation energy. State what is meant by the term activation energy.

The activation energy is the minimum Energy for a reaction to occur (i)

(2)

State what is meant by the term rate of reaction.

___frequency of successful collisions

11

(1)

(1)

c)

State the Collision Theory and explain, in terms of particles, why, at a fixed temperature, you might expect the rate of this reaction to double when the concentration of sodium thiosulfate is doubled and the concentration of hydrochloric acid remains the same. (You may use a diagram to assist you.) (4) Twice as many / double number of particles (NOT molecules) 1

More / twice / double (effective) collisions (in a given time) OR Double / greater / increased collision frequency

12

Enthalpy (kJ)

Question 19 Consider the energy profile diagram shown below.

(4 marks)

1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 Progress of reaction

a)

(i)

State the value of H for this reaction

 H = Hp – Hr = 300-950 = - 650 kJ mol -1

b)

13

[1]

(ii)

Classify this reaction as endothermic or exothermic.Exothermic

[1]

(i)

On the graph, label ‘activation energy’.

[1]

(ii)

State the value of Ea for this reaction. Ea = 1400 - 950 = 450 kJ mol -1

[1]...