HCl as a Primary Standard?

Question: Why is HCl not suitable as a primary standard?
Answer:  There are three main reasons why HCl is not suitable as a primary standard:

• HCl is not a solid at room temperature and pressure. 
• HCl cannot be obtained at a very high purity.
• HCl does not have a high molecular mass.

You can find out more about what makes, and does not make, a primary standard at:
http://www.ausetute.com.au/titrstand.html

Which Element has the Smallest Atomic Radius?

Question: Write the symbol for the element which has the smallest atomic radius Na, Si, Mg, P.

Answer: In general, atomic radius decreases going across a period of the Periodic Table.
Sodium (Na), magnesium (Mg), silicon (Si) and phosphorus (P) all belong to the third period.
In order of increasing atomic number they are: Na (Z=11), Mg (Z=12), Si (Z=14), P(Z=15)
Therefore, in order of decreasing atomic radius they are: Na > Mg > Si > P
So, phosphorus, symbol P, has the smallest atomic radius.

Read more about trends in atomic radius at AUS-e-TUTE: http://www.ausetute.com.au/trendar.html

Number of elements in period 2

Question: Give the number of elements in period 2 of the periodic table
Answer: 8

The rows going from left to right across the Periodic Table are called Periods.
The periods are numbered from 1 at the top to 7 on the bottom.
The first period contains only 2 elements: hydrogen and helium.
The second period contains 8 elements: lithium, beryllium, boron, carbon, nitrogen, oxygen,  fluorine and neon.

Find out more about how the periodic table is arranged at http://www.ausetute.com.au/pertable.html

Find more about the elements making up Period 2 at http://www.ausetute.com.au/trendpd2.html