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Here, a primary standard is typically a reagent which can be weighed easily, and which is so pure that its weight is truly representative of the number of moles of substance contained. Features of a primary standard include: High purity; Stability (low reactivity) Low hygroscopicity (to minimize weight changes due to humidity)
The volume of a particular material or compound is affected by ambient moisture and may be considered its coefficient of hygroscopic expansion (CHE) (also referred to as CME, or coefficient of moisture expansion) or the coefficient of hygroscopic contraction (CHC)—the difference between the two terms being a difference in sign convention.
Flat boat dish is an oblong, flat-bottomed dish, in which it is easy to weigh out the substance, and then move it the reaction chamber, but is not recommended for hygroscopic or air-reactive samples. A tall-shaped dish - it is elongated, oblong, flat-bottomed dish, used when the solid is transferred without a funnel .
The toxicity of this compound is similar to toxicity of choline itself, which is fairly low, and it is used as a dietary supplement. Oral LD 50 value for a human is estimated to be 200 to 400 grams (as choline). Nevertheless, choline bitartrate can be harmful, if absorbed through skin. It may cause skin, eye and respiratory system irritation.
The Physikalisch-Technische Bundesanstalt (PTB) is the national metrology institute of the Federal Republic of Germany, with scientific and technical service tasks.It is a higher federal authority and a public-law institution directly under federal government control, without legal capacity, under the auspices of the Federal Ministry for Economic Affairs and Climate Action.
KHP is slightly acidic, and it is often used as a primary standard for acid–base titrations because it is solid and air-stable, making it easy to weigh accurately. It is not hygroscopic. [4] [5] [6] It is also used as a primary standard for calibrating pH meters because, besides the properties just mentioned, its pH in solution is very stable.
Dynamic vapor sorption (DVS) is a gravimetric technique that measures how quickly and how much of a solvent is absorbed by a sample such as a dry powder absorbing water. It does this by varying the vapor concentration surrounding the sample and measuring the change in mass which this produces.
Mass fraction can also be expressed, with a denominator of 100, as percentage by mass (in commercial contexts often called percentage by weight, abbreviated wt.% or % w/w; see mass versus weight). It is one way of expressing the composition of a mixture in a dimensionless size ; mole fraction (percentage by moles , mol%) and volume fraction ...