17

You have three types of errors: The errors in the accuracy of your measurement. Assuming you are reading the water levels consistently (at eye level at the bottom of the meniscus), these should be random. To add random, uncorrelated errors, the standard method is to sum their squares and take the square root. So, for the 0.1 mL average error for the 10 mL ...


10

Good to see classical analytical chemistry queries. These graduated pipettes or Mohr pipettes they are called, confuse even the relatively advanced users. First you have to check where the graduations end. If the pipette was meant to deliver 10 mL or 50 mL you should not see 10 or 50 mL mark near the tip of the pipette. That is one hint. Add a picture of the ...


8

Keep in mind that a graduated cylinder is never meant for accurate volume transfer. You would probably use a Class-A 100 mL buret to transfer 70 mL to a vessel if accuracy were that critical say, 70.0 mL was desired. All these general chemistry rules of thumbs are not useful for real analytical work. Experimental numbers matter the most. Let us assume you ...


6

Elsewhere here, M. Farooq has given excellent answer for this analytical chemistry question. I like to explore this answer by explaining what are these lines means and some confusions arose from M. Farooq's answer. The pipette is an important tool in many fields of science. There are few types of them: Volumetric pipettes: This type of pipettes is used to ...


3

This sort of derivation is a just painful, but straightforward. As Poutnik mentioned it is just a series of equations where you eliminate variables by substitution. So start with the basics. $\ce{HA <=> H+ + A-}\tag{A}$ $\ce{BOH <=> B+ + OH-}\tag{B}$ $\ce{H2O <=> H+ + OH-}\tag{C}$ Given: $\mathrm{C_A}$ is the concentration of the HA ...


2

Let's take your questions one at a time. Are there any alternative ways to purify primary amines from a complex mixture that I am unaware of? Your end application is LC-MS. There are plenty of papers on amine-specific derivatization methods for metabolome analysis. For example, there is one by Zhao et al. [1]. Instead of purifying the primary amine ...


2

Meanwhile, the mark scheme says that one must use the 100 ml cylinder, for the 10 ml cylinder would give a total 7*0.1/10=7% percentage uncertainty, compared to the 1.4% from the 100 ml cylinder. (1.4% < 7%) Let's simplify the problem and say the 10 mL cylinder has a +1% systematic error (and there is no random error), i.e. delivers 10.1 mL when filled ...


1

You can use reducing agents to reduce the $\ce{SeO3^2-}$ salt to elemental selenium. This paper1 discusses the use of iron(II) salts in acidic medium (phosphoric - hydrochloric acid) as reducing agent. The reaction proceeds at r.t. You can use other reducing agents like hydrochloric acid, sulfur dioxide, hydroxylamine hydrochloride, hydrazine hydrochloride. ...


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