scitf measuresments a calculations Flashcards
Give a general description of measurement units
- Units used in scientific measurements are the units of the «metric system»
- First developed in France and accepted internationally in 1960.
- Called SI units and composed of 7 base units.
- Prefixes are used to indicate decimal fractions or multiples of various units
Name the SI base units (physical quantity, name of unit, and abbreviation)
- Mass, kilogram, kg
- length, meter, m
- time, second, s^a
- temperature, kelvin, K
- amount of substances, mole, mol
- electric current (elk. storm), ampere, A
- luminous intensity (Lichtintensität), candela, cd
For what are prefixes used? Name them
- to indicate decimal fractions or multiples of various units
- Giga, G, 10^9
- Mega, M, 10^6
- kilo, k, 10^3
- deci, d, 10^-1
- centi, c, 10^-2
- milli, m, 10^-3
- micro,μ^a , 10^-6
- nano, n, 10^-9
- pico, p, 10^-12
- femto, f, 10^-15
How does heat flow? How can you calculate Kelvin, C° , F by having C°, or Kelvin?
- heat always flows spontaneously from a substance at higher temperature to one at lower temperature
- Zero on the Kelvin scale is the lowest attainable temperature, -273.15°C, referred to as «absolute zero»
- K = oC + 273.15
- °C = 5/9 (F – 32)
- T(°F) =T(°C) × 9/5 + 32
How is the volume of a cube given? Order graduated cylinder, syringe (Spritze), buret, pipet, flask depending on volume
- The volume of a cube is given by its length cubed, (length)^3
- 1 L = 1 dm3 = 1000 cm3 = 1000 mL
- Syringe, buret, pipet > graduated cylinder > flask
How is the density defined?
- It is the amount of mass in a unit volume of the substance:
- > Density = mass / volume
- The density of water is 1.00 g/cm3
What is stoichiometry?
- Using a balanced chemical equation to calculate amounts of reactants and products is called stoichiometry
- 1700s Lavoisier: law of conservation of mass
How is a chemical equations?
- Determine the reactants and the products through experiments
- Derive the chemical formulas
- Write the unbalanced equation
- Balance the equation by adding coefficients
What are the steps in stoichiometry?
- first calculate n
- > n= m/M
- n (1.reactant) is equal to (2. Reactant) (amount has to be payed attention)
- calculate m with formula -> m= M*n
How do alkali metals react?
- Elements in the same group show similar reactivities
- All alkali metals, when reacting with water, form their hydroxides and hydrogen
What happens during combustion reactions?
- Combustion (Verbrennung) reactions are fast reactions producing fire; most contain oxygen in the air as a reactant
- During combustion, hydrocarbons (s.a. CH4) react with oxygen(2O2) to produce CO2 and H2O.
- Compounds containing O in addition to C and H also produce CO2 and H2O during combustion (ex: glucose)
Give the reaction for potassium with water
-2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
How does an airbag work?
- Decomposition of sodium azide (NaN3) inflates the car airbags
- Due to collision, NaN3 decomposes very quickly and produces the nitrogen gas (N2) which inflates the airbag
- 2NaN3 (s) -> 2Na (s) + 3N2 (g)
How is amu (atomic mass unit) defined? How is molecular weight defined?
- 1 amu=1,66054x10^-24g and 1 g=6,02214x10^23 amu
- Amu was defined by assigning 12 amu to carbon-12 isotope
- Many elements are found in nature as a mixture of their isotopes
- Molecular weight: total mass of atoms in the chemical formula
- For ionic substances we use the term formula weight rather than molecular weight.
What is 1 mole?
- amount of substance that contains as many objects (atom, molecule, etc.) as there are atoms in 12 g of carbon-12
- 1 mole 12C atoms = 6.02 x 10^23 ^12C atoms
- 1 mole H2O molecules = 6.02 x 10^23 H2O molecules
