Quantitive Chemistry Flashcards
(17 cards)
What is the law on conservation of mass?
The products formed in a reaction is the same as the total of the reactants used.
How to calculate the relative formula mass
Add together all the relative atomic masses (top numbers) for all the elements in the formula.
Why is mass conserved during chemical reactions?
No atoms are lost or made in the reaction.
How to calculate the percentage composition by mass
Percentage Composition = (Molar Mass of Element / Molar Mass of Compound) × 100
What is a closed system?
Substances cannot enter or leave the system
What is an example of closed systems
Test tubes, flasks with bungs on and precipitation rections
What happens in a precipitation reaction?
An insoluble solid forms when two solutions are mixed.
What is an open (non-enclosed) system?
Reactants are free to enter and products are free to leave.
What is apparent increases in mass (mass changes with gas)
When a metal reacts with oxygen to produce metal oxide. This is because when oxygen combines with metal atoms.
What is Apparent decrease in mass
Mass appears to decrease in thermal decomposition. A metal breaks down to form metal oxide and carbon dioxide, which escapes into the air.
What is there always about results of chemical measurements?
Uncertainty
What is resolution of an instrument in chemical measurements?
The smallest change in the reaction that can be shown.
E.g. 0.1g in a digital balance reading to 1 d.p.
1mm in a ruler divided into tenths of a cm.
What value is uncertainty given in
Plus or minus +
-
How does uncertainty depend on the type of instrument and resolution?
(Digital and scale)
Digital instrument: uncertainty is equal to plus or minus half the resolution
Instrument with a scale: uncertainty is equal to scale.
What is the concentration of a solution?
How much a solute a given volume contains.
How do you convert cm³ to dm³
Divide by 1000
