Please help me classify these...?

Question

Question 1: Is steel a mixture or a compound?

Question 2: If an atom of an element has 69 neutrons and 50 electrons, it's mass number is:
a) 119
b) 69
c)50
d)19
e) none of these

Note: Mass number is the number of protons and neutrons. I thought the answer was a, 119 but then I realised wouldn't it depend what charge the atom was which would altar the electrons and protons (they may not be the same)? Is it e, none of these or a?

Question 3:
Is magnetising a screw driver a chemical and physcial change or only a physical change? What about kicking a football and also production of sound by the vocal cords?

Thankyou for helping.

Answer 1

Lauren --
1) Steel is a solid mixture (alloy) of Iron and Carbon (but often containing Nickel, Chromium, Manganese and/or other elements as well).

2) The key to this question is that it says "atom" not "ion". You are correct that the answer is 119. In an ion there can be more or less electrons than protons, but in an atom (which is neutral), the number of electrons must always equal the number of protons.

3) This is a trick question. Your teacher probably wants you to say that these are all physical changes. Here is how all three could also be considered chemical changes:

Magnetising a screw driver requires that the steel blade of the screw driver be moved through a magnetic field. If a person holds the screw driver and moves it, then the persons muscles are involve and moving a muscle requires chemical changes. If a robot did this, then perhaps it would be only a physical change.

Kicking a football and the production of sound by the vocal cords both also require muscle activity. Once again, the contraction of muscles requires chemical changes.

Answer 2

1. Steel is an an alloy of Iron. (It cannot said to be compound but an alloy is a mixture of metals)

2. Mass number is the sum of protons an neutrons. The no. of protons is equal to the number of electrons. So mass number is 119. What you first thought was right.

3. Magnetising the screw driver is not a chemical change. No change as such is done to its composition. The other two phenomena are also temporary changes in shape (hence can be considered as a physical change - but after a few moments the original shape is regained)

Answer 3

1. Is an mixture (an alloy of metals)

2. a.
Because if it has 50 electrons it ill have 50 protons and mass of proton = 1. So its 69 + 50 = 119

3 They are all physical changes.

Answer 4

1. Steel is a mixture
2. B electrons have nothing to do with atomic mass.
3. they are all physical change. their chemical composition has not changed, just their vibrations. now go to bed