Calculations - Need to be shown method

[Asterix]

1. How much malachite green (in g) must be dissolved in 300ml such that 20ml diluted to 100ml produces a 1 in 200 solution.
3. What weight of potassium permangate is required to prepare 100ml of a solution such that when one part is diluted 8 times a 1 in 4000 solution is produced.
4. How many millilitres of water must be added to 180ml of a 40% v/v solution in order to produce a 5% v/v solution.
5. What is the strength of the final product when 100ml of a 10% solution is added to 300ml of 5% and 100ml of a 7.5% solutions.
6. Magnesium trisicllate contains 5% each of mg trisicilate, light magnseium bicarbonate and sodium bicarbonate. How much of these ingredients is contained in 150ml.

[Nik]

I didn't think "calculations season" on the forum started until october Anyway i'll start you off on the first one.

The way I would do this would be to say the amount you're after you should call x(g), i.e x(g)/300ml. 20ml would therefore contain x/15(g) which is then diluted to 100ml. This is equivalent to a 1 in 200 solution.

So if x/15(g) is in 100ml, then 2x/15(g) is in 200ml.

So 2x/15(g) = 1g. Therefore x =..... i'll let you do this because it's so easy.

I appreciate the method is a bit unusual but it works for me.

[DavidS]

I'd like to see the chemical formula of Magnesium Bicarbonate

[johnep]

Believe that magnesium bicarbonate or something like it was a component of 'gripe water'. I would like to know the chemical name for Malachite. Is it a basic copper carbonate? What is it used for in medicine these days?
johnep

[shan]

1. How much malachite green (in g) must be dissolved in 300ml such that 20ml diluted to 100ml produces a 1 in 200 solution.7.5g
3. What weight of potassium permangate is required to prepare 100ml of a solution such that when one part is diluted 8 times a 1 in 4000 solution is produced.20g
4. How many millilitres of water must be added to 180ml of a 40% v/v solution in order to produce a 5% v/v solution.1260ml
5. What is the strength of the final product when 100ml of a 10% solution is added to 300ml of 5% and 100ml of a 7.5% solutions.6.5%
6. Magnesium trisicllate contains 5% each of mg trisicilate, light magnseium bicarbonate and sodium bicarbonate. How much of these ingredients is contained in 150ml. 7.5g each

The answer I worked out are in red.

Hope I am right.

Shan

[Nik]

I reckon the first answer's correct shan.

[shan]

I reckon the first answer's correct shan.

What about the rest of the answers?

Shan

[shan]

1. How much malachite green (in g) must be dissolved in 300ml such that 20ml diluted to 100ml produces a 1 in 200 solution. 1 in 200 is 0.5 in 100, i.e. 0.5 in 20ml ==> 300 X .5/20 = 7.5g in 300ml
3. What weight of potassium permangate is required to prepare 100ml of a solution such that when one part is diluted 8 times a 1 in 4000 solution is produced.1 in 4000 is 0.025g in 100 hence before dilution 1 part will have 8 X 0.025 =0.2g. so 100ml of the solution will have 0.2 X 100 = 20g
4. How many millilitres of water must be added to 180ml of a 40% v/v solution in order to produce a 5% v/v solution.40% : 5% is 1: 8 so we need to dilute it 8 times or add 7 X 180 = 1260mls of water
5. What is the strength of the final product when 100ml of a 10% solution is added to 300ml of 5% and 100ml of a 7.5% solutions.10% in 100ml = 10g, 5% in 300ml = 15g, 7.5% in 100ml = 7.5g. So add all will give 32.5g in 500ml hence 100mls will have 32.5/5 = 6.5g =6.5%
6. Magnesium trisicllate contains 5% each of mg trisicilate, light magnseium bicarbonate and sodium bicarbonate. How much of these ingredients is contained in 150ml. 5% of each = 5 X 150/100 = 7.5g in 150ml

Well this is how I worked them out

Shan

[Nik]

I didn't really want to do all the answers for him just the first to start him off. I reckon you've probably got the rest of them right though.

[shan]

What weight of potassium permangate is required to prepare 100ml of a solution such that when one part is diluted 8 times a 1 in 4000 solution is produced.1 in 4000 is 0.025g in 100 hence before dilution 1 part will have 8 X 0.025 =0.2g. so 100ml of the solution will have 0.2 X 100 = 20g

-- I think it is 0.2g not 20 g. logic is 0.2g in 100mls is 0.002g in 1ml. So 1 in 4000 is 0.002g in 8ml (1X8/4000).