Advanced Higher Chemistry 2018-19

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Reply 80

lois_____

Thank you!! Why are you putting 20/60 tho ?

Original post by _nim1

The KOH is diluted as 40cm3 is added so you need to find the new concentration if that makes sense

Reply 81

lois_____

Aw I see now tyty :smile:

Original post by lois_____

Thank you!! Why are you putting 20/60 tho ?

Reply 82

_nim1

20cm3 of KOH divided by the new total volume of 60cm3 then multiply that by the concentration. That’s how you find the concentration of solutions that are diluted : )

Original post by lois_____

Thank you!! Why are you putting 20/60 tho ?

Reply 83

Mhussain01

For the same question how do you find the H+ conc?

Original post by _nim1

20cm3 of KOH divided by the new total volume of 60cm3 then multiply that by the concentration. That’s how you find the concentration of solutions that are diluted : )

Reply 84

_nim1

Find the ph using ph= pka - log[acid]/[salt]
Then use the equation ph= -log[H+] just rearranging it

Original post by Mhussain01

For the same question how do you find the H+ conc?

Reply 85

A_Ch

Does anyone have the answers to yesterday's scholar session?

Reply 86

Labrador99

Volunteer Team

Original post by A_Ch

Does anyone have the answers to yesterday's scholar session?

@SCHOLARuk are you able to help?

Reply 87

lois_____

Anyone know how to do q4 ?

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Reply 88

chic geek

Original post by _nim1

thank you so much x

Reply 89

chic geek

how did you get 0.66 for the concentration of salt?

Original post by _nim1

Find the ph using ph= pka - log[acid]/[salt]
Then use the equation ph= -log[H+] just rearranging it

Reply 90

chic geek

can anyone help me with these?

5. When one mole of phosphorus pentachloride was heated to 523K in a closed vessel, 50% dissociated as shown
PCl5(g) -> PCl3(g) + Cl2(g)
How many moles of gas were present in the equilibrium mixture?
A 0·5 B 1·0 C 1·5 D 2·0

7. Which of the following 0.01 mol l−1 aqueous solutions has the highest pH value?
A Sodium fluoride
B Sodium benzoate
C Sodium propanoate
D Sodium methanoate

10. Which of the following reactions would show the greatest decrease in entropy?
A H2(g) + F2(g) → 2HF(g)
B KNO3(s) → KNO2(s) + 1/2 O2(g)
C CO3^2−(aq) + 2H+(aq) → H2O(l) + CO2(g)
D CO3^2−(aq) + CO2(g) + H2O(l) → 2HCO^3−(aq)

20. Which of the following compounds would liberate one mole of hydrogen gas if one mole of it reacts with two moles of sodium?
A C2H5OH
B HOCH2CH2OH
C CH3COOH
D CH3CHO

Reply 91

A_Ch

For question 20, I think the answer is B because the reaction between a metal and an alcohol is an elimination reaction which removes the one hydrogen atom to make an alkene and if there are 2 moles of sodium then you would be looking for the molecule with 2 hydroxyl functional groups. Thats what I would do.

Reply 92

A_Ch

Can I get help on these questions please.

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Reply 93

lois_____

Scholar answers

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Reply 94

A_Ch

Thank you!! :h:

Original post by lois_____

Scholar answers

Reply 95

_nim1

The concentration of the salt is 0.333 from the answer to part a)
The concentration of the acid is 0.667, found by 40/60 multiplied by the concentration which is 1

Original post by chic geek

how did you get 0.66 for the concentration of salt?

Reply 96

lois_____

I think for the 2nd one, to get the right chloride ion concentration you’d need a total volume of 100ml but you’ve already got 25ml there so 100-25 = 75ml so wld need to be diluted by 75ml of water. So 75ml is the answer I would think

Original post by A_Ch

Can I get help on these questions please.