Some basic Concepts Of Chemistry- SI Units & Scientific Notation

1.      Base Physical Quantities & their Units Base Physical Quantity (symbol) Length (l) Mass (m) Time (t) Electric current (I) Thermodynamic temperature (T) Amount of substance (n) Luminous intensity (Iv) Name of SI Unit (symbol) metre (m) kilogram (kg) second (s) ampere (A) kelvin (K) mole (mol) cd 2. Prefixes used to indicate the multiples or submultiples of a unit- Multiple deka-101 hecto-102 kilo-103 mega-106 giga -109 tera-1012 Submultiple deci-10-1 centi-10-2 milli-10-3 micro-10-6 nano-10-9 pico-10-12
3. Temperature: i.                    F= 9/5(0C) + 32 ii.                  K= 0C + 273.15
4.  Scientific notation: any number can be represented in the form N × 10n, where  n is an exponent having positive or negative values. N is a number (called digit term) which varies between 1.000... & 9.999.... Example: i.                    We can write 232.508 as 2.32508x10-2in scientific notation. (Note: while writing it, the decimal had to be moved to the left by two places and same is the exponent (2) of 10 in the scientific notation.) ii.                  0.00016 can be written as 1.6x10-4 (Note: the decimal has to be moved four places to the right and ( – 4) is the exponent in the scientific notation.)
Multiplication and Division (5.6x105)x(6.9x108)=(5.6x6.9)x(105+8) =38.64x1013 =3.864x1014	Addition & Subtraction: i.                    First the numbers are written in such a way that they have same exponents ii.                  After that the coefficients are added or subtracted as case may be. Example -I: 6.65x104 + 8.95x103=6.65x104 + 0.895x104(exponent is made same for both the numbers) =(6.65 + 0.895)x104 (The numbers can be added now) = 7.545x104 Example -II: 2.5×10-2 – 4.8 × 10-3 = (2.5 × 10-2) – (0.48 × 10-2) = (2.5 – 0.48) × 10–2 = 2.02 × 10–2
QUESTION: 1.The basic quantity in the International system of units, is a. electric current    b. mole and light intensity   c. time and temperature  d. all 2.10-12, is called: a. pico             b. giga          c. mega    d. tera    3.  The thickness of a micron, is               a. 10-6m   b.10-3m    c.10-12m     d.10-9m  4.Every measurement consists of a number and a :  a. standard.       b. decimal    c. exponent     d. unit.   5. In the SI system, the basic unit of measurement for mass is the:                  a. tonne     b. metre    c. kilogram    d. pound  6. 5x10-5 can also be written as:                     a. 0.50000       b. 0.000005    c. 0.00005    d. 0.0005       7. Convert 25 g to mg.  a. 250 mg   b. 2500 mg      c. 25 000 mg   d. 250 000 mg 8. The prefix (micro) means:  a. 0.000 001   b. 0.01    c. 0.001    d. 0.1 9. 1 kg = -------------- mg. 10. The SI unit for time is- a. millisecond   b. light year   c. year    d. second 11. The SI unit for length is- a. centimeter    b. kilometer    c. foot   d. meter _________________________________________________________________________________ Ans:  1.d(All)   ,     2. a (pico),  3.a(10-6m),  4.d (unit),  5.c(kilogram),  6.c(0.00005) ,7.c(25000mg), 8.a (0.000001),  9.1000000mg, 11.d(second)