Lecture 1: Chemistry introduction Flashcards
Is there any structural formula for NaCl? Justify your answer.
Is there any structural formula for NaCl? Justify your answer.
No because it is an ionic compound. Not a covalent bond. (You cant just have a molecule, you have ions.)
What is a molecular compound and an ionic compound?
Molecular Compounds are formed due to covalent bond between elements, while Ionic Compound is formed due to electrostatic force of attraction known as Ionic bond.
What is the definition of a Mol?
1 mol is the number of atoms in exactly 12g of carbon-12. (6 x 10^23 atoms)
Why are molar masses not presented as an integer in the periodic table?
The molar mass is a measure of the average molecular mass of all the molecules in a sample.
Write the chemical, molecular and structural formula of ethanol (2 carbons, six hydrogens and one oxygen).
How do you calculate Molarity?
How many grams of NaCl in water is in each of the following three flasks? How many grams of water is in each of the three flasks?
A: There are 2 mols therefore their mass = 2*58.44g
B: There are 1 mol therefore its mass = 58.44g
C: 58.44g/2
How do you prepare a solution of a soluble salt? Describe the steps and explain.
- put the salt
- put the water
- dissolve everything
- Then top it up to the top to the marker line.
Any idea why we do that?
because when you dissolve the salt the salt dissolves
If you have 1l of a 5Molar solution of NaCl and need 300ml of a 2 Molar solution, how would you make the required solution?
volume = 1l
initial concentration = 5M
CinitialVinitial=CfinalVfinal
Therefore 1000mlx5M=5000
= vol x 2M
5000/2 = Volume = 2500l
Therefore add 1500l of water and divide it by 1500/300ml
Indicate what each arrow represents as a period property of the periodic table.
Ionization energy: the energy to take an electron out
Electron Affinity: The force to attraction electrons
Atomic radius: the size of atoms increases down the periodic table
The nucleus reduces as the proton and neutrons increase
What does the octet rule say and how does this rule explain ionic and covalent bonds?
Octet rule: in covalent bond formation, atoms go as far as possible towards completing their octets by sharing electron pairs.
•Non-metallic elements form covalent bonds to one another by sharing pairs of electrons.
What is a polar bond? Give an example.
A polar bond is a covalent bond between two atoms where the electrons forming the bond are unequally distributed. This causes the molecule to have a slight electrical dipole moment where one end is slightly positive and the other is slightly negative.h20
Why do ethanol and acetone dissolve in water?
because ethanol and acetone are polar molecules with an arrangement such that the polar bonds are arranged in space so that the dipoles do not cancel out. They are able to attract their unequal dipoles to the dipoles in water molecules which are also polar.
Enthalpy is defined as H = U + PV.
Why in biology and chemistry is enthalpy variation most of the times defined as ΔH = q, and what does q mean?
because you never have a variation in pressure as it is a closed system.
and u=q+w and workdone is usually 0 as well in biology and chemistry.
What is a spontaneous process?
one that occurs without the addition of external energy.
What does the second law of thermodynamics state?
that the entropy of the universe always increases for a spontaneous process.
In the phase diagram below, where can you find 5 phases in equilibrium?
the point between j k l h and i.
On the phase diagram below, choose a point where you have liquid in equilibrium with the gas phase, and write down the composition of each phase.
%liquid = D2/D1+D2
%vapor=D1/D1+D2
