ST. AUGUSTINE'S GRAMMAR SCHOOL, MANCHESTER

Answer all questions. For questions I — 10, write down the letter of your choice on your answer sheet, for the rest of the questions a written explanation is required.

Section A. For each numbered phrase select the one heading which is most closely related to it. Each heading may be used one, more than once, or not at all.

Q 1—5 Choose from the following:

1. The mass in grammes of 0.25 moles of oxygen atoms, 0.
2. The number of moles of carbon atoms C. present in 3 g or carbon.
3. The number of moles of hydrogen atoms H. present in 9g of water.
4. The number of moles of calcium atoms Ca. having the same number of atoms as 0.5 moles of silver atoms Ag.
5. The number of grammes of helium having the same number of atoms as 0.5 moles of silver atoms Ag.

Section B. Each of the questions or incomplete statements in this section is followed by five suggested answers. You are to select the best answer in each case.

Q6. Carbon dioxide gas is about 1.5 times as dense as nitrogen gas. Suppose that a gas jar of nitrogen was placed on top of a gas jar of carbon dioxide with the open ends together. Which of the following would you expect to have happened after a while?

1. The two gases would not have mixed at all.
2. Some of the carbon dioxide would have moved into the gas jar containing nitrogen, but none of the nitrogen would have moved into the gas jar containing carbon dioxide.
3. Some of the nitrogen would have moved into the gas jar containing carbon dioxide but none of the carbon dioxide would have moved into the gas jar containing nitrogen.
4. Some of each gas would have moved into the gas jar containing the other.
5. The two gases would have reacted with one another.

Q7. Which of the following statements is true?

1. Equal masses of elements contain equal number of atoms.
2. A mole of atoms is the number of atoms present in 1g of an element.
3. One mole of atoms of any e1ement contains the same number of atoms.
4. The mass in grammes of one mole of any element is always a whole number.
5. It is necessary to tine a mole as the standard unit of amount of an element because it is not possible to find the real masses of atoms.

Q8. John Dalton first introduced the idea of atomic mass in the early nineteenth century. He regarded the atomic mass of an element as —

1. the number of times heavier an atom of that element is than a hydrogen molecule.
2. the number of times heavier the molecule of that element is than a molecule of hydrogen is.
3. the mass of an atom of that element compared with the mass of an atom of hydrogen.
4. the number of tines heavier an atom of that element as a particle of hydrogen.
5. the true mass of an element.

Q9. 0.75 of a metal X was found to react with 0.32 g of oxygen. The atomic mass of X is 75. The formula of the compound termed was —

Q1O. The simplest formula at a compound containing by mass 65.63% of iron and 36.36% of sulphur.

Section C. Answer all questions.
Q11.
The table shows the atomic masses and atomic numbers of atoms labeled T to Z.

1. How many protons are there in an atom of Y?
2. How many electrons are there in an atom of W?
3. How many neutrons are there in an atom of Z?
4. Which atoms are isotopes of the same element?
5. Which atom would readily form an ion with a single positive charge?
6. Which is an atom of a noble gas?

Q12. Explain simply the difference between electrovalency and covalency. Illustrate your answer by reference to sodium chloride and ammonia. Briefly describe two simple experiments which could help you to decide if the bonding in a given solid compound was electrovalent or covalent.

 

Q13. Define molar solution. Describe how to perform the titration of hydrochloric acid against sodium hydroxide solution whose molarity is known, naming the equpment and indicator you would use. In this titration it was found that 20cm³ of HCl exactly neutralised 25cm³ of 1 MnaOH (sic). Write equation for the reaction, and calculate the molarity of hydrochloric acid.

Q14. Draw and label the apparatus which would be suitable for reducing copper(II)oxide. Write a balanced equation for the reaction. What is the appearance of the substance before and after passing hydrogen (or other reducing gas) through the heated substance. What steps would you take in order to calculate the simplest formula of the substance? Why is it necessary to continue to pass hydrogen through the sample after the reaction is complete and the external heating had stopped.

Q15. 1. Calculate the mass of ZnSO₄ which is produced by using 6.5 g of zinc with excess dilute H₂S0₄.

2. Calculate the gramme—molecular mass of ZnSO₄ and H₂S0₄
3. Write a balanced equation.
4. Name the gas which is produced in this reaction.
5. How would you test for this gas?