Chemistry: Heat treatment of metal practical and questions Task

Aim: To investigate the malleability of quenched and annealed metals.

Materials:

· Three similar sewing needles.

· Two pairs of pliers.

· A heat source, such as a gas flame or hotplate.

· A cup of iced water.

Safety:

· Wear safety glasses during this experiment.

Method:

1. Using the pliers hold the first needle and flex it slightly to get the feel of its elasticity.

2. Heat the centre if the second needle in the hottest part of a flame, so that it is red hot, and then drop it in the iced water. Take it out and try the elasticity. Does it spring back when flexed the same amount as before?

Flex the unheated needle a similar amount. Is there any difference in the brittleness between the heated and unheated needles?

Break both needles. Compare the hardness at the breaks. Record your observations

Observations: ·

3. Take the third unheated needle and heat it until it is red hot. This time remove it gradually from the flame so that the centre part cools slowly, over about two minutes. When it is cool try bending it. Does it spring back, bend permanently or break?

Take this last needle again, heat it red hot, and then quench it in cold water. Then heat it again less strongly until almost red hot, and then cool gradually over two minutes.

Flex the needle. Is there any difference in the brittleness between this needle and the other two needles?

Observations:

Break the needle. Compare the hardness at the break. Record your observations.

Prac Questions:

1. Name the three processes used in this experiment .

2. Explain how the rate of cooling affects the brittleness and size of the crystals formed.

3. Explain in terms of bonding why quenching metals are harder than unquenched metals?

4. Explain why it is difficult to straighten a bent metal coat hanger

Theory Questions:

1. In 2 mole of NO2

a) How many mole of N atoms are there?

b) How many mole of O atoms are there?

c) Calculate the number of O atoms.

2. Work out the molar mass of the following compounds.

a) Magnesium chloride, MgCI2

b) Sodium acetate, NaCH3COOH

c) Iron (II) phosphate, Fe3(PO4)2

3. 

a) Work out the molar mass of methane, CH4

b) Use your answer to (a) to work out:

(i) The mass of 2 mol CH4

(ii) The mass of H atoms in 2 mol CH4

4. 

a) Work out the molar mass of water, H2O

b) Use your answer to (a) to work out the number of mol in:

(i) 125grams of water.

(ii) 5kg of water.

5. 

(a) Breifly state how you input numbers in standard form on your calculator. For example, how would you input the number 5×10^12

b ) Use your calculator to work out the number of mol contained in:

(i) 3.10×10^23 molecules of octane.

(ii) 2.408×10^24 molecules of nitrogen.

6. Work out the percentage composition of all the elements in Ni2(SO4)3

Show your working.

7.  In 3 mole of C3H8 molecules:

a) How many moles of C atoms are there?

b) How many mole of H atoms are there?

c) Calculate the number of C atoms.

d) Calculate the number of H atoms.

8.  a) Which contains the greater number of molecules:

1 mole C2H6 or 2 mole I2?

b) Which contains the greater number of atoms:

2 mole MgCl2 or 2 mole O2?

9.  Work out the mass of 2.6mole of Mg3(PO4)2

10.  a) How many mole are contained in 4.2×10^25 molecules of methanol, CH3OH?

b) Work out the mass of the methanol.

11. Work out the percentage of water in the compound ZnSO4 . 4H20

12. a) What are some of the limitations of the “metallic lattice” model for metals?

b) How does the “ball bearing” model explain why some metals bend more easily than others do?