i need help in chemistry

i need help in chemistry

Introductory Chemistry

Assessment Item 2

Question 1

The following paragraph is a fictional description of the hypothetical element Rokhampium.

Rokhampium (Rk) is a silvery, dense substance that conducts electricity and can be drawn into thin wire or beaten into thin sheets. It has 21 protons in its nucleus. The sample of rokhampium that I have in the laboratory also has 24 neutrons in the nucleus. I can remove an electron from each atom in one mole of rokhampium by applying 631 kJ of energy.

Answer the following questions about rokhampium giving reasons for your answers. Do not use the Periodic Table or the internet for information – all the information you require is supplied in this question (if you Google for the answer, you will not learn how to work it out for yourself and may end up being wrong).

Note that the reasons are more important than the correct answer so they should be comprehensive. (1 mark each – half for the answer and half for the reason)

I. What is the atomic number of Rk? The atomic number is 21, because the atomic number equals the number of protons present in the nucleus.

II. What is the mass number of the isotope that I have? The mass number of the isotope would be 45 because atomic mass equals the combined sum of neutrons and protons found in the nucleus.

How many electrons are there in each atom of Rk? In each atom of Rk, there are 21 electrons, Elements are present in zero oxidation states, therefore, to be neutral atom, protons and electrons must be in equal number.

III. Draw the Bohr electronic configuration of Rk.

IV. What is the valency of Rk likely to be?

V. How might Rk react with Cl – show using a Lewis diagram?

VI. What type of ion will Rk form?

VII. What is the ionisation energy of Rk?

VIII. What type of substance is Rk in its elemental form?

IX. What will one mole of Rk weigh?

(10 marks)

Question 2

Sodium chloride (NaCl), table salt, is an ionic compound, while ammonia (NH3), present in many cleaning compounds, is a covalent compound.

a) Define a compound. (2 marks)

b) Describe the different types of bonding in these two common household substances and why they form in these instances. (2 marks)

c) Comment on the physical properties of ionic compounds. (1 mark)

d) Demonstrate the formation of the bonds in each compound using Lewis diagrams. (2 marks)

(7 marks)

Question 3

Balance the following equations:

a) H2SO4 + Zn(NO3)2 → ZnSO4 + HNO3

b) KClO3 → KCl + O2

c) P4O10 + H2O → H3PO4

d) K3PO4 + Ca(NO3)2 → KNO3 + Ca3(PO4)2

e) NH3 + O2 → NO + H2O

(5 marks)

Question 4

Perform the following simple chemical reaction.

· Place 1 teaspoon of bicarbonate of soda (NaHCO3) in a glass and dissolve it in 50 mL water. Note the smell and taste.

· Note the smell and taste of vinegar (CH3COOH)

· Slowly add vinegar to the bicarbonate of soda solution while stirring until no more bubbles form.

· Note the smell and taste of the resulting solution.

a) Describe the reaction including the smell and taste of the reactants and the products.

(3 marks)

b) The reaction that occurred is:

NaHCO3(aq) + CH3COOH(aq) → NaCH3COO(aq) + H2O(l) + CO2↑

1. Balance the equation.

2. Name the products of the reaction.

3. What do the symbols (aq) and ↑ indicate about the products of this reaction?

4. What was responsible for the bubbles you observed?

5. What type of chemical reaction might this be classified as?

(5 marks)
Question 5

I could get a similar reaction by using vinegar and washing soda (Na2CO3). If you have some washing soda you might like to try it but don’t taste the washing soda!

The reaction is:

Na2CO3(aq) + CH3COOH(aq) → NaCH3COO(aq) + H2O(l) + CO2(g)

1. Balance the equation. (2 marks)

2. Give the chemical name for washing soda. (1 mark)

3. What is the molecular mass of washing soda? (2 marks)

4. How many moles of washing soda are there in 5 g? (2 marks)

5. If 5 g of washing soda is dissolved in 100 mL water what is the concentration of the solution in mol/L? (3 marks)

6. If 5 g washing soda reacts, how many moles of CO2 will be produced? (2 marks)

7. What will this amount of CO2 weigh? (3 marks)

(15 marks)

Question 6

a) Classify the following reactions as exothermic or endothermic reactions (2 marks):

a. Melting solder

b. Cooking a cake

c. Breaking down glucose in muscles

d. Reacting magnesium and oxygen in a flash bulb

b) Define a catalyst and discuss how it controls the rate of a reaction using a graph (do not copy/paste the graph from anywhere – you must redraw the graph). Remember to explain what the graph represents. (3 marks)

(5 marks)

Total: 50 marks.