Gravimetric questions

[bedigursimran]

Hey guys.

We were doing a prac for chemistry and I had a found a few questions that may come up on the SAC but I don't know them. Would you guys (please) be able to help me?

Here are the steps of the prac:

Spoiler

Step 1: Accurately weigh about 1.0 g of the fine powder and place it in a 100 mL beaker. Record the mass of the fertiliser and beaker. 

Step 2 : Add about 50 mL of distilled water to dissolve all the sulfate in the fertiliser, then filter the mixture into a 600 mL beaker. Wash the residue thoroughly. 

Step 3 : Add 3.00 mL of 2.0 M HCl to the filtrate and make it up to 200 mL with distilled water. Heat the solution over a Bunsen burner and bring it to boil. Remove the Bunsen burner and add 15.0 mL of 0.5 M BaCl2. A white precipitate of BaSO4  will form. 

Step 4 : Return the beaker to the heat and continue to boil for another minute. Remove the beaker from the heat and allow to stand until the precipitate settles. Add a drop or two of 0.5 M BaCl2. If a precipitate forms add 3.0 mL of 0.5 M BaCl2 if no precipitate forms proceed to the next step.
 
Step 5 : Weigh and record the mass of a round filter paper.
 
Step 6 : Place the filter paper in the funnel of a vacuum filtration unit and wet with distilled water. 

Step 7 : Filter the solution in the 600 mL beaker using the vacuum filtration unit making sure to collect al the precipitate in the filter paper. Wash the precipitate with distilled water. 

Step 8 : After the final washing collect a sample of the filtrate and test it by adding one drop of 0.1 M AgNO3. If a white precipitate forms continue to wash the precipitate in the filter paper with distilled water. 

Step 9 : Allow the filter paper to dry overnight and weigh on an electronic balance.

Here are the questions:

Why is HCl added(step 3)?
What is the balanced equation for the reaction between H+ and CO32-?
Why is it important for the precipitate to have a high molecular formula?

Thanks so much for helping!!

[belb]

sorry I don't really explain things with the correct terminology so check them but question
iii) High molar mass means you can calculate moles more accurately becuase you're working with bigger numbers
i) hcl is added to acidify the solution of fertiliser so only the so4 2- ions are precipitated out by the bacl2 solution- ie by acidifying the solution the hcl reacts with the co3 2- ions present and therefore produces co2 (g) water so.. baso4 is the only precipitate and there's no baco3 precipitate to alter the results

check if I'm right though not 100% sure sorry haha and you could've done the sac already but good to know for the future I guess haha