Write chemical equations for the action

[Fly_High]

Hi guys, I need your help:


A white solid V is heated strongly. At a high temperature, V gives off carbon dioxide and changes to a solid W that begins to glow.

When water is added to W, it begins to fizz, produces heat and crumbles to a powder X.

X dissolves in water to form an alkaline solution Y.

When carbon dioxide is passed into solution Y, the solution turns cloudy. The cloudiness is caused by a white suspension Z and its formation is used as a test for carbon dioxide.

(a) Deduce the identity of V, W, X, Y and Z, giving either their chemical or common names.

(b) Write chemical equations for the action of:

(i) heat on V,

(ii) carbon dioxide on solution Y.

(c) State a use for either W or X.


Please help me solve this 2 problems, I really don't know how to do. Thanks.

 

[cristo]

IF this is a homework question, you should at least put down some of your thoughts before we can help you. For part (a) think of the tests for common chemicals.

 

[Fly_High]

I can't cos I really don't understand the whole question. I am blur and confused with the whole question.

 

[Fly_High]

Wait...I look thru the question again...

 

[Fly_High]

Since V gives off carbon dioxide, it should be a carbonate.

V is a white solid, so it should be aluminium, calcium, lead or zinc.

X dissolves in water, it must be soluble in water so it should consists of nitrate, chloride or sulphate salts.

That's all I know.

 

[cristo]

Ok, I'll give you a hint. To test for CO2 we normally add Y to the CO2. This will form Z (the reason for the solution becoming cloudy). The common name for Y is limewater. If you can find the chemical name for Y, and hence Z, you are on the right track.

 

[cristo]

Since V gives off carbon dioxide, it should be a carbonate.

Good

V is a white solid, so it should be aluminium, calcium, lead or zinc.

X dissolves in water, it must be soluble in water so it should consists of nitrate, chloride or sulphate salts.

Think again about this. Following my above hint, X when dissolved in water, produces Y, limewater. If you find the chemical name for this, then you will be able to work out X, V and W. Z can be found by the formula limewater+CO2->...

 

[Fly_High]

I know! Z should be calcium carbonate, right?

For V, X and W, I still can't work out...

 

[cristo]

I know! Z should be calcium carbonate, right?

Correct

For V, X and W, I still can't work out...

I'm not sure how many more hints I can give. Let's recap some of the things you said.

Since V gives off carbon dioxide, it should be a carbonate

Which carbonate do you think it is? (NB: there's nothing in the question to say that V, W, X, Y & Z are distinct)

Now, V decomposes into CO₂ and W. If you find V, then a simple equation will give the form of W. When water is added to W, a solid X is produced, which then dissolves in water to form Y, limewater (or Ca(OH)_{2 (aq)})

 

[Gokul43201]

Cristo, you've been incredibly patient to this point, and it's good to see fly_high showing effort as well. I'd like to stress however, that really, the ONLY good way to proceed with questions like this is by writing the equations at every point that a species is identified. Else, the whole exercise becomes a disconnected mess of ideas.

So, to fly_high: first, write down the equation that describes the formation of a cloudy suspension in limewater upon bubbling CO2 through it.

 

[Fly_High]

I have worked out the answer, but I am unsure whether it is correct...

V: KCO3 (potassium carbonate)

W: K (potassium)

X: KOH (potassium hydroxide)

Y: Calcium

Z: Calcium carbonate

 

[Gokul43201]

...X dissolves in water to form an alkaline solution Y.

X: KOH (potassium hydroxide)

Y: Calcium

Can you dissolve KOH in water and get a solution of Ca? Is it even possible to have a solution of Ca in water?

Z is correct. Start from there. Write down the equation for the formation of calcium carbonate. You can even look up this equation simply by Googling "calcium carbonate carbon dioxide white suspension."

This will, however, only get you through this particular problem. You'll only run into more trouble unless you learn the fundamental concepts.