Is money concrete or abstract?

A while ago my dad gave me a fifty dollar bill and told me to spend it on groceries. Later in the day I spent fifty dollars on gas. My dad protested, saying that he wanted me to spend that 50 dollars on groceries.

I was puzzled by this. If I my dad gives me fifty dollars and I use the exact same note to buy gas this kind of makes sense, but it should't matter. It depends on how you think of money. Is money a physical note like paper currency or it is an abstract number like your money in your bank account? Two fifty dollar notes are different, because they are made of different atoms, were minted at different times, in various states of wear. Money in the bank has no such discriminating features; it is just an abstract number.

My dad's complaint would have made less sense if he had given me one 50 dollar note and I had used a different 50 dollar note to pay for gas. I could mark the one my dad gave me and say, "I am saving the note you gave me for groceries", but if money is just an abstract number denoting wealth having no physical existence, then that 50 dollars could have been spent on the groceries or the gas.

The confusion between myself and my dad was that I thought of physical notes as loosing their identity when they go in my wallet, like they do at the bank.

If my dad deposits 50 dollars in my bank account and then tells me to spend that 50 dollars on groceries then my dad's logic makes even less sense. Money in the bank is an abstract number. I can't look in my bank account and fish out the exact 50 dollars that he originally deposited in my bank account.

So 50 dollars cash is the same as fifty dollars in my bank account, but also different. Is it a fallacy speak of digital money as if it is physical and vice versa?

Admit it, you spent 50 bucks on the newly legal cannabis in your state. Smoked it, then decided to type this post...I get it. I've been there. You are definitely a better grocery shopper when you have the munchies.....
p.s. My response is totally to deflect away from the issue because I too spent some bread on newly legalized pot in my state and am currently too blitzed to follow what you're asking...However, I do know you can buy concrete with paper money or bank account money.

I think money in general is an abstract concept. Societies incorporated money to simplify bartering, where two pounds of wheat was two pounds of wheat and a goat was a goat. Money is a representation of wealth; people no longer need to carry around wheat or goats to trade. They can use the value of the wheat or goats instead.

Was your father protesting because you didn't spend money on groceries at all, that instead you spent it on gas? That would make the argument:

I gave you $50 to spend on groceries.
You spent $50 on gas.
You spent nothing on groceries.
Therefore, you didn't do as I asked.

In that case, whether money is abstract or concrete makes no difference. Your father gave you $50 in exchange for groceries (that he was essentially going to give right back to you), and you had no groceries.