Atoms, compounds, and ions

Introduction to the atom

• 1 Mole=6.02*10²³ = Avogadro's number
• 1 Mole(6.02*10²³) of ¹²C atoms in 12g of C
• mole's role: switching between amu and g
• 1g=1mole of amu=6.02*10²³amu
• 1more of ²⁷AI=27grams
• 1mole of ⁵⁶Fe=56grams
• A(mass number)=Z(atomic number=proton number)+N(neutron number)
• ¹⁸Fe^- consists of: 9 proton, 9 neutron, 10 electron

ions and compounds

• in covalent bonds, atoms share electrons
• a group of atoms joined by covalent bonds is a molecule
• there is NO such thing as a molecule of an ionic bond
• in ion bonds, electrons are fully transferred between two atoms, so that ions are formed
• ionic bond: two oppositely charged ions attract each other
• 
• representing molecules: chemical formula, structural formula
• *the group 3A elements link

names and formulas of ionic compounds

• cation: ion with net positive charge
• anion: ion with net negative charge
• predicting charges on monatomic cations and anions
• groups 1,2,13,14: usually give away valence electrons to become ions(C is sometimes an exception)
• groups 15,16,17: usually negative charge, because is more likely to gain electrons not lose
• most of the transition metals(d-block)are polyvalent
• naming of transition metal cation: chromium(II)chloride=Cr²⁺
• naming anions: add suffix '-ide'
• formulas and naming of basic ionic compounds: 

1. always name the cation(+)before the anion(-)
2. when naming the cation, don't include the word ion or charge unless it's a polyvalent ion
3. any ionic compounds have a net charge of zero(they cancle each other)

• polyatomic ions: the ion that contains more than one atom
• polyatomic ion is formed when a neutral molecule(covalent bond) gain or lose electrons
• the chemical formula of calcium hydroxide is: Ca(OH)2 not CaOH2

Isotopes and mass spectrometry 

• isotope: same # of proton, electron but different # of neutron
• atomic weights: weighted average calculated by summing up each isotope's atomic mass
• mass number=number of netrons+number of protons(atomic number)
• 1u(amu)=1/12 of the mass of single neutral atom of carbon-12 *12 is the mass #
• mass of a neutron=1amu
• mass of a proton=1amu
• mass of an electron=considered to be zero amu
• atomic mass=how many protons and neutrons*1amu(not exact, but close)

article summary: the principles of pH

source: https://byo.com/malt/item/1494-the-principles-of-ph

pH change that happens during the mashing

• mashing=precipitation of phosphates(found in brewing water)+amino acids derived(taken) from the malt
• phosphoric acid(H3PO4) disassociate
• (if calcium ions are present)calcium phosphate disassociate, leaving behind hydrogen ions
• higher(than 10^-7mol/L) H+ concentration in a solution=acidic link
• (if magnesium ions are present)magnesium phosphate do the same thing, but the effect on pH is less dramatic
• if calcium sulfate is added, the calcium ions react with the amino acid group(present within the solution)then leave behind hydrogen ions
• these changes in mineral composition+the precipitation of calcium salts->pH decrease(prior to fermentation)
• the carbonate(CO3-2), bicarbonate(HCO3-) ions act as buffers to pH decrease

Proper mash pH

• optimal pH of an infusion mash: 5.2~5.6
• high pH during the mash increase the amount of dextrins, less fermentable wort
• polyphenols(such as tannins), silica compounds easily extracted under high pH: instability, astringency*
• *when sparging, pH of the last running climbs to 5.8~6.0, stop the sparging

Controlling Mash pH

• with lots of carbonate ions in the water(high mash pH): 
• add calcium ions from gypsum(calcium sulfate) or calcium chloride
• or add organic acids(phosphoric acid, lactic acid)
• if a brewer is using very soft water(low mash pH):
• add a little bit of chalk(calcium carbonate), baking soda(sodium bicarbonate)
• link Understanding residual alkalinity&pH

The importance of boil pH

• during the boil, calcium phosphate continue to be precipitated
• optimal post-boil wort pH: 5.0~5.2
• Maillard reactions are not favored at lower pH(for light colored beer)
• to lower pH, add a little bit of calcium(gypsum, calcium chloride, acid)

Fermentation

• optimal ending pH less than 4.4(larger 4.2~4.6, ale 3.8)
• during fermentation, pH continue to drop: 
• yeast take in ammonium ions(strongly basic) and excrete organic acids

other helpful articles

Residual Alkalinity and pH for All Grain Beer Brewing

Effective hardness=Ca(ppm)/1.4+Mg(ppm)/1.7

RA=Alkalinity(as CaCO3)-Effective hardness or (50*Bicarbonate)/61-Effective hardness

Residual alkalinity and mash pH

full size Residual Alkalinity Nomograph link