#### Important formulae :

1. $$No\ of\ moles =\frac{mass}{Molar\ mass}$$
2. $$No\ of\ moles\ of\ gas=\frac{Volume\ at\ STP}{22.4}$$
3. $$No\ of\ moles\ of\ Particles=\frac{No\ of\ Particles}{6.023\times 10^{23}}$$
4. $$No\ of\ moles\ of\ solute=Molarity \times Vol(L)$$
5. $$Eq.\ wt.\ of\ a\ salt=\frac{M.W.\ of\ salt}{Total\ +ve\ \ charge\ of\ metal\ ion}$$
6. $$Eq.\ wt.\ of\ element=\frac{Atomic\ Weight}{Valency}$$
7. $$Avg.\ atomic\ mass=\frac{m\times a+n\times b}{m+n}$$ where, a + b are atomic masses and m + n are precentage.
8. $$\%\ of\ element\ in\ compound =\frac{n(at\ mass\ of\ element)}{MW\ of\ compound}\times 100$$ where, n= No. of atoms of that element
9. $$Molarity=\frac{w\times 1000}{M.W.\times V(ml)}$$
10. $$Normality=\frac{w\times 1000}{E.W.\times V(ml)}$$
11. $$Molality=\frac{w\times 1000}{M.W.\times W(g)}$$ W = Weight of solvent
12. $$Mole\ fraction(X)=\frac{n}{n+N}$$
13. $$\%W/W=\frac{W\times 100}{W+W_{0}}$$
14. $$ppm=\frac{weight(vol)\ of\ solute\times 10^{6}}{weight(vol)\ of\ solution}$$
15. $$Molecalar\ weight =2\times V.D.$$
16. $$Eq.\ wt.\ of\ metal=\frac{Wt.\ of\ metal}{wt.\ of\ H_{2}\ displaced}\times 1.008$$
17. $$Eq.\ wt.\ of\ metal=\frac{Wt.\ of\ metal\times 11200}{Vol\ of\ H_{2}\ displaced\ at\ STP (mL)}$$
18. $$Eq.\ wt.\ of\ metal=\frac{Wt.\ of\ metal\times 35.5}{Wt.\ of\ Chlorine\ combined}$$
19. $$Eq.\ wt.\ of\ metal=\frac{Wt.\ of\ metal\times 11200}{Vol\ of\ Cl_{2}\ combined\ at\ STP (mL)}$$
20. $$Eq.\ wt.\ of\ metal=\frac{Wt.\ of\ metal\times 8}{Wt.\ of\ oxygen\ combined}$$
21. $$Eq.\ wt.\ of\ metal=\frac{Wt.\ of\ metal\times 5600}{Vol\ of\ O_{2}\ displaced\ at\ STP (mL)}$$
22. $$Molority=\frac{\%W/W\times density\times 10}{Molecular\ weight}$$
23. $$M_{1}V_{1}=M_{2}V_{2}\ (Molarity\ equation)$$
24. $$N_{1}V_{1}=N_{2}V_{2}\ (Normality\ equation)$$
25. $$n=\frac{Molecular\ weight}{Empirical\ formula\ Weight}$$
26. $$^{\circ}F=\frac{9}{2}(^{\circ}C)+32$$
27. $$K=^{\circ}C+273.15$$
28. $$1L=1dm^{3},\ 1mL=1cm^{3}$$

#### Important Facts :

1. Antoine Lavoisier - Law of conservation of mass
2. Joseph proust - Law of definite proportions
3. John Dalton - Law of Multiple proportions
4. Richter - Law of combining weights.
5. Gay Lussac - Law of combining Volumes.
6. $$1\ amu=1.6605\times 10^{-23}\ gram$$
7. $$Mass\ of\ C\ atom=1.9926\times 10^{-23}\ gram$$
8. $$Avogadro's\ number(N_{A})=6.022\times 10^{23}$$
9. AZT = Azido thymidine,drug used for aids victims.
10. The limiting reagent is the reagent that is entirely consumed when a reaction goes to completion. Its amount limits the amount of the product formed.

#### Precision and Accuracy.

The term precision refers for the closeness of the set of values obtained form identical measurements of a quantity.

Accuracy refers to the closeness of a single measurement to its true value.

Let us take an example to illustrute. this. Three students were asked to determine the mass of a piece of metal where mass is known to be 0.520g. Data obtained by each Student are recorded in table below

 Student Mesurements in g. 1 2 3 Average A 0.521 0.515 0.509 0.515 B 0.516 0.515 0.514 0.515 C 0.521 0.500 0.520 0.520

The data for student A are neither, precise nor accurate. The data for student B are precise but not accurate. The data for student C are both precise and accurate.