Chem lab questions

1) Primary standard is substances that can be readily dissolve in water to give a known molarity of solution. It is stable, not deliquescent(do not absorb moisture in air) and efflorescent(do not lose water upon exposure to air).
2)High molar mass can reduce estimating error as the error in mole is smaller.
As mole=mass/molar mass, the higher the molar mass, the less will the error of mass affect the mole.
3) The alkali solution inside the burette will eventually become more and more concentrated as water will evaporate. The concentrated alkali will corrode the inner glass surface of burette, making it thinner( but not making holes). As the volume of the burette is higher, the reading on the burette is therefore inaccurate.

2009-10-12 20:37:27 補充：
primary standard(usually solid) also should have a known mass and purity.

1.
Primary standard solution 姐係佢有一個 stable composition.唔會 easily decompose 同埋轉個 molarity (有 d acid 如 conc.sulphuric acid 會吸水而改變 molarity).有已知的 purity,mass,volume.

2.
有 higher molar mass 定 molarity?
molarity 的話係因為有高 d 就可以做 dilution.如果 molarity 低就做唔到大 molarity 的 solution了.