Question 1:
Atoms in pure iron are arranged in an orderly manner and in layers.
(a) What is the effect of atom arrangement in pure iron on the ductility and malleability of the metal?
(b) Iron alloy can be made by mixing some carbon into molten iron. How does the arrangement of atoms in the iron alloy affect the hardness of the alloy?
Answer:
(a) When a force is applied, the layers of atoms slide over each other. Pure metal is soft, that is ductile and malleable.
(b) Foreign atoms (carbon atom) disturb the orderly arrangement of atoms in pure iron. The layers of atoms are harder to move or slide over each other. Thus the addition of carbon strengthens the structure of iron and makes iron stronger and harder.
Atoms in pure iron are arranged in an orderly manner and in layers.
(a) What is the effect of atom arrangement in pure iron on the ductility and malleability of the metal?
(b) Iron alloy can be made by mixing some carbon into molten iron. How does the arrangement of atoms in the iron alloy affect the hardness of the alloy?
Answer:
(a) When a force is applied, the layers of atoms slide over each other. Pure metal is soft, that is ductile and malleable.
(b) Foreign atoms (carbon atom) disturb the orderly arrangement of atoms in pure iron. The layers of atoms are harder to move or slide over each other. Thus the addition of carbon strengthens the structure of iron and makes iron stronger and harder.
Question 2:
The purity of gold is measured in carats (K). 24 carat gold is pure gold without the addition of any other metal whereas 18 K gold is a mixture comprising of 18 units by mass of gold with 6 units by mass of other metal such as copper.
(a) What is the role of copper in 18 K gold?
(b) Calculate the composition percentage by mass in 24 g of 18 K gold.
Answer:
(a) To make gold harder and stronger
(b)
$$ \% \text { gold }=\frac{18}{24} \times 100=75 \% ; $$
$$ \% \text { copper }=\frac{6}{24} \times 100=25 \% $$
The purity of gold is measured in carats (K). 24 carat gold is pure gold without the addition of any other metal whereas 18 K gold is a mixture comprising of 18 units by mass of gold with 6 units by mass of other metal such as copper.
(a) What is the role of copper in 18 K gold?
(b) Calculate the composition percentage by mass in 24 g of 18 K gold.
Answer:
(a) To make gold harder and stronger
(b)
$$ \% \text { gold }=\frac{18}{24} \times 100=75 \% ; $$
$$ \% \text { copper }=\frac{6}{24} \times 100=25 \% $$
Question 3:
Justify the following statements:
(a) Stainless steel is used to make washing machines
(b) High voltage electric cables are made from aluminium alloy
(c) 18 K gold is used to make rings
Answer:
(a) Washing machines are in contact with water. Water and oxygen cause metals to rust. Stainless steel is resistant to corrosion.
(b) Electrical cables are hung on tall poles. Aluminium alloy has low density.
(c) Pure gold is soft. Gold alloy is harder and stronger.
Justify the following statements:
(a) Stainless steel is used to make washing machines
(b) High voltage electric cables are made from aluminium alloy
(c) 18 K gold is used to make rings
Answer:
(a) Washing machines are in contact with water. Water and oxygen cause metals to rust. Stainless steel is resistant to corrosion.
(b) Electrical cables are hung on tall poles. Aluminium alloy has low density.
(c) Pure gold is soft. Gold alloy is harder and stronger.