Help with AS level chemistry questions ?

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Report Thread starter 5 years ago
Hi i'm doing amount of substance in chemistry, I understand the work that we did and the experiment went well however we have been given homework which I have absolutely no idea on what to do I've searched everywhere and cannot find anything please help ?

The questions you need the answers from previous questions so I can't do anything as I can't do the first question please help me so I can hopefully finish it off myself.

QUESTION: (sorry its long)

Indigestion tablets contain sodium hydrogen carbonate plus other substances including flavouring, sugar and insoluble material to help form the powdered ingredients into a tablet.

The purpose of this titration is to analyse some solution made from the tablets to find out the percentage by mass of sodium hydrogen carbonate in the tablet.

9.73g of indigestion tablets were crushed up in mortar and pestle. The resulting powder was dissolved in a beaker of distilled water. The solution was filtered to remove any insoluble material and the filtered tablets were washed with more distilled water. The solution was placed into a volumetric flash and made up 1dm^3 and labelled 'x'.

Titrate the indigestion tablet solution 'x' against the standardised 0.1M hydrochloric acid until you have 2 readings which are concordant.

1) Calculate the average titre from your results ?

2) Write an equation for the reaction between HCl and sodium hydrogen carbonate which releases CO2 & water.

Sorry its a long question the rest of the questions follows question 1 such as working moles etc which I want to give a go myself but please help me starting im so lost. Thank you for your time

Yes I posted this twice as i put it in the wrong forum before and I really need help as I can't finish my homework otherwise, thank you
Badges: 12
Report 5 years ago
Let's start with question 1. A titre is the volume of the HCl required to complete the titration. It follows, then, that average titre is the average of the concordant (close together) values that you've gotten. So if you got, for example 20.4 cm3 and 20.3 cm3, that's pretty much concordant since there's only a 0.1 difference between them. You could try again to ensure you couldn't achieve an identical result (i.e. 20.3cm3 or 20.4cm3), but this is sufficient. So, to work out the average, you do:

The sum of the terms

The number of terms

So, in the above example, we do:

20.4 + 20.3


This gives you 20.35cm3. With your results, you'll obviously have a different value, but this is still your average titre.

As for question 2, it can be difficult to visualise the answer, but let's start with what we know. I'll assume you're confused with sodium hydrogen carbonate.

(?) + HCl -----> CO2 + H2O

Now, for sodium hydrogen carbonate. Sodium is Na, hydrogen is H and a carbonate group is represented by CO3 (think limestone - calcium carbonate - from GCSE - CaCO3). Guess what? That's exactly what sodium hydrogen carbonate is: NaHCO3. Let's add that to the equation.

NaHCO3 + HCl -----> CO2 + H2O

From your GCSE knowledge of carbonates, you know that reacting a metal carbonate with an acid produces salt, water and carbon dioxide. This is also the same for metal hydrogen carbonates, like NaHCO3.

A salt is defined as a substance formed when an acid has a hydrogen atom replaced by a metal atom. There's a further circumstance which gives a salt, but this is not needed for the question. If you take the knowledge of:

Metal hydrogen carbonate ---> A salt + water + carbon dioxide

It should be easy for you to complete the question. As a hint, 'make' what you already know, then put together what's left over. For example, to make water, you need 2 hydrogen atoms and 1 oxygen atom, so take this out of the 'reactants'. Once you've done this for carbon dioxide, you'll perhaps be able to see what the salt you form is. Remember, you need to replace the H in the acid with a metal.

Your last stage is to write the equation, using state symbols. (s) indicates a solid, which includes precipitates, (l) is a liquid, (g) is a gas and (aq) indicates a solid that is suspended in a liquid. You may not need state symbols for this question, but it doesn't harm you to learn to use them and to be honest, it is good form. Once you add the state symbols to the equation, and add the salt, you will have the answer, which is the below equation. I will use (S) to show a state symbol is needed:

NaHCO3(S) + HCl (S) ----> A salt (S) + H2O(S) + CO2(S)

If you need any more help, don't hesitate to contact me c:

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