Chemistry, 11.07.2019 23:30, kyle65

Flouride is known to prevent tooth decay so it is added to the city water supply for drinking. a medium sized city is populated with 150,000 people. each person uses approximately 660.0 l of water each day. how many kg of naf must be added to the water supply each year to have the required flouride concentration of 1.0 ppm?

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answered: Katiecool290

3.6 × 10^4 kg NaF

Step 1. Calculate the daily volume of water used

Volume = 150 000 persons × (660.0 L/1 person) = 9.90 × 10^7 L

Step 2. Calculate the daily mass of the water

Mass of water = 9.90 × 10^7 L water× (1.00 kg water water/1 L water)

= 9.90 × 10^7 kg water

Step 3. Calculate the daily mass of NaF

Daily mass of NaF = 9.90 × 10^7 kg water × (1.0 kg NaF/10^6 kg water)

= 99.0 kg NaF

Step 4. Calculate the yearly mass of NaF

Yearly mass of NaF = (99.0 kg NaF/1 day) × (365.25 days/1 yr)

= 3.6 × 10^4 kg NaF

answered: Guest

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

answered: Guest

assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the $3d$ have energy higher than those in the $4 s$ orbital while lower than those of the $4 p$ orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the $4s$ orbital is therefore filled right after $3p$ orbitals and before $3 d$ orbitals.

potassium has electron configuration $[\text{ar}] 4 s^{1}$ and calcium $[\text{ar}] 4 s^{2}$ . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration $[\text{ar}] 4 s^{2} \; 3d^{1}$ and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the $ns^{2} \; (n-1) p^{1}$ and should be highlighted as well.

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Flouride is known to prevent tooth decay so it is added to the city water supply for drinking. a med...