Only question #4, I put question #2 as a refrence only. 2.Calculate the number o

Question

Only question #4, I put question #2 as a refrence only.

2.Calculate the number of moles of sodium carbonate present in a mixture of sodium bicarbonate, sodium carbonate and a neutral component if 6.0 ml of 0.100 M HCl were used to titrate 0.200 g of this mixture with phenolphthalein as the indicator.

4. Calculate the number of moles of sodium bicarbonate originally present in the unknown mixture in question 2, knowing that 15.0ml of 0.100 M HCl were used in step 2 of the titration, Using methyl orange as the indicator.

Please show a step by step process.

Explanation / Answer

4. I FORGOT SOMETHING:

for the 2nd part of the titration, bicarbonate ion is being neutralized to carbonic acid, a weakly acidic substance, whose pH is matched by the methyl orange indicator, which changes color in a weakly acidic solution. Each mole of acid neutralizes one mole of bicarbonate.

0.015L * 0.1mole/L = moles acid = moles of bicarbonate ion = moles of sodium bicarbonate

= 0.0015moles = 1.5*10^-3 moles of sodium bicarbonate.
HOWEVER, 0.0006 moles of carbonate were present, which I forgot.

0.0015 - 0.0006 = 0.0009 moles = 9*10-4 moles of sodium bicarbonate are initially present. Because the other part is sodium carbonate, which is still hanging around for this 2nd part of the titration!

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