This a question regarding Chemistry and I really need help, like, NOW.

A sample of 0.195g of potassium was added to 500 cm3 of cold water. when the reaction was finished, 100 cm3 of 0.100mol/dm 3 of hcl acid was added to form solution X.

.i)Calculate the number of moles of hydroxide ions formed when the potassium was added to water.

.ii) calculate the no. of moles of hydrogen ions in 100 cm3 of 0.100mol/dm3 hcl acid.

.iii) give an ionic equation to represent the neutralisation reaction.

.iv) Suggest a ph value for solution X and explain the answer.

Reply 1

Protoxylic

14

Can you show us where you are going wrong or are getting stuck?

Reply 2

barbruh

OP

11

I am actually confused how to find the number of moles from here (is the formula mol = volume x concentration ?), and hydroxide ions, and hydrogen ions- How can we find the number of moles of them? I'm fully lost with this whole question, so a little help on every question would be appreciated.

Reply 3

Protoxylic

14

Original post by barbruh

I am actually confused how to find the number of moles from here (is the formula mol = volume x concentration ?), and hydroxide ions, and hydrogen ions- How can we find the number of moles of them? I'm fully lost with this whole question, so a little help on every question would be appreciated.

First of all, writing the equation of the reaction between potassium and water would be a good start. And you know the mass of potassium, so you can work out the number of moles of potassium. The water is in huge excess, you can tell because the volume of water is 500cm^3 which is roughly 500g as the density of water is 1g/cm^3. So all of the potassium will react to give potassium hydroxide, find out the mole ratio in the equation and that will give you the answer to a) given that all of the potassium hydroxide dissociates to give 1 mole of hydroxide ions per mole of potassium hydroxide.

Reply 4

Stiff Little Fingers

21

Original post by barbruh

I am actually confused how to find the number of moles from here (is the formula mol = volume x concentration ?), and hydroxide ions, and hydrogen ions- How can we find the number of moles of them? I'm fully lost with this whole question, so a little help on every question would be appreciated.

To work out the mols of Hydroxide ions, think how Potassium reacts with water, or rather what the reaction product would be - you calculate it from the potassium:hydroxide ratio, rather than directly. So calculate the moles of potassium and then the number of moles of hydroxide you'd need to react with that.

Reply 5

barbruh

OP

11

So, what could be the answers to iii) no. and iv) no.

Reply 6

Stiff Little Fingers

21

Original post by barbruh

So, what could be the answers to iii) no. and iv) no.

For three, think what the neutralisation reaction would be - KOH and HCl are your reactants - KOH is a base, HCl is an acid - remember that acid + base = water + salt, so your molecular equation is KOH + HCl -> H2O + KCl. To convert to an ionic equation, think which of those are in aqueous state and would exist as the ionic compounds.

This a question regarding Chemistry and I really need help, like, NOW.

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