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    I just started year 12 chemistry and I need the answers to:

    1.Explain why hydrated sodium carbonate and sodium hydroxide are not appropraite bases for making up a standard solution

    I don't understand these questions, how am I supposed to work these out?

    2.The burette has a maximum uncertainty of +-0.05 cm^3 in each reading. Calculate the percentage uncertainty in your first accurate titre. (my first accurate titre was 30.40cm^3).

    3. The volumetric flask has a maximum uncertainty of +-0.3cm^3 and the pipette has a maximum uncertainty of +-0.04cm^3. Which of these gives the larger percentage uncertainty
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    Sorry you've not had any responses about this. Are you sure you've posted in the right place? Here's a link to our subject forum which should help get you more responses if you post there.


    Just quoting in Fox Corner so she can move the thread if needed :wizard:
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    1) Both of these compounds are highly hygroscopic (absorb moisture from the air) so you cannot weigh out precise masses of them properly, as the powder you use will contain an unknown amount of water.

    2) Percentage uncertainty is the absolute uncertainty (the +- part) divided by your reading, for example if you measured 50cm3 and the absolute uncertainty was +-0.05cm3, percentage uncertainty would be 0.05/50 = 0.1%. (remember that you multiply decimals by 100 to get percentages).

    3) Same concept as 2. Use the value that you measured out with that piece of equipment divided by the absolute uncertainty of that equipment.
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    (Original post by Frank Peters)
    I just started year 12 chemistry and I need the answers to:

    1.Explain why hydrated sodium carbonate and sodium hydroxide are not appropraite bases for making up a standard solution

    I don't understand these questions, how am I supposed to work these out?

    2.The burette has a maximum uncertainty of +-0.05 cm^3 in each reading. Calculate the percentage uncertainty in your first accurate titre. (my first accurate titre was 30.40cm^3).

    3. The volumetric flask has a maximum uncertainty of +-0.3cm^3 and the pipette has a maximum uncertainty of +-0.04cm^3. Which of these gives the larger percentage uncertainty

    The entire point of a standard solution is that its concentration must be known. Sodium hydroxide solutions are hygroscopic, meaning that it absorbs CO2 from the air. This would alter the concentration of NaOH, as some is converted to NaHCO3, hence it's inappropriate for use as a standard. Hydrated Na2CO3 loses water to the environment and hence its mass changes; it's also an inappropriate compound to use as a standard.

    Percentage uncertainty/error is the %error/recorded value x 100. Calculate this for the volumetric flask and the pipette, the larger value has the largest percentage uncertainty.

    Hope this helps!
 
 
 
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